zen trace analysis support (#945)

Integrates the **tourist** trace analysis library and builds a full `zen trace` command suite for working with Unreal Engine `.utrace` files.

### Trace analysis library (`thirdparty/tourist/`)
- Adds the tourist library as a third-party dependency with three modules: **foundation** (platform primitives, memory, scheduling), **trace** (UE Trace protocol decoding), and **analysis** (event dispatching and analyzer framework).
- Cross-platform support for Windows, Linux, and macOS.

### `zen trace` CLI commands (`src/zen/cmds/`, `src/zen/trace/`)
- **`zen trace analyze`** — Summarize a `.utrace` file: session metadata, thread inventory, command line + build configuration, CPU profiling scopes, timing, event rates, log messages, and (with symbols) memory allocation metrics including live-allocs dumps, callstack-keyed aggregation, and allocation churn. Optional HTML output for memory reports.
- **`zen trace inspect`** — Dump the event schema (declared types, fields, sizes) from a trace file.
- **`zen trace trim`** — Extract a time-window from a trace into a new `.utrace` file.
- **`zen trace serve`** — Launch a local HTTP server hosting an interactive trace viewer; opens in the default browser.

### Symbolication (`src/zen/trace/symbol_resolver.*`, `thirdparty/raw_pdb/`)
- Pluggable resolver with multiple backends: `pdb` (in-tree raw_pdb), `dbghelp` (Windows), `llvm-symbolizer` (all platforms), `atos` (macOS). An `auto` backend picks the best available tool per platform.
- Microsoft Symbol Server support: downloads PDBs on demand using a redirect-aware HTTP client.
- Local PDB cache keyed by image GUID preserves symbols across binary recompilation.
- Callstack trimming heuristic strips UE internal noise from reports.
- Binary analysis cache (`.ucache_z`) avoids re-resolving the same trace.

### Interactive trace viewer (`src/zen/frontend/html/`, `src/zen/trace/trace_viewer_service.*`)
- Timeline: scope-level detail, horizontal zoom/pan, vertical scrolling, viewport-driven loading with pre-computed LOD for responsive navigation of large traces.
- Thread grouping (collapsible sidebar sections) synthesized from name suffixes, natural sort order, visual distinction between lane threads and OS threads.
- Bookmark and region annotations; region categories with per-category toggles; bookmark marker toggle in the toolbar.
- Filterable Logs tab showing captured `UE_LOG` output.
- Stats tab with per-scope aggregate statistics.
- Memory tab with interactive allocation analysis and an allocation size histogram.
- CsvProfiler event parsing and chart UI.

### Other in-branch supporting changes
- **Cross-platform browser launcher** (`browser_launcher.{h,cpp}`) used by `trace serve`.
- **`ReciprocalU64`** fast 64-bit integer division (zencore/intmath) for trace analyzers.
- **`parallelsort`** cross-platform parallel sort helper (zenutil).
- Frontend zip build rule so the viewer's HTML assets are bundled into `zen.exe`.
- `/Zo` flag for better optimized debug info on Windows release builds.
- `trace-tests.cpp` in the `zen-test` harness (harness itself landed on main via #985).

1 files changed, 140 insertions, 0 deletions

diff --git a/thirdparty/raw_pdb/src/PDB_IPIStream.cpp b/thirdparty/raw_pdb/src/PDB_IPIStream.cpp
new file mode 100644
index 000000000..dfd21bc56
--- /dev/null
+++ b/thirdparty/raw_pdb/src/PDB_IPIStream.cpp
@@ -0,0 +1,140 @@
+// Copyright 2011-2022, Molecular Matters GmbH <[email protected]>
+// See LICENSE.txt for licensing details (2-clause BSD License: https://opensource.org/licenses/BSD-2-Clause)
+
+#include "PDB_PCH.h"
+#include "PDB_IPIStream.h"
+#include "PDB_RawFile.h"
+#include "PDB_Util.h"
+#include "PDB_DirectMSFStream.h"
+#include "PDB_InfoStream.h"
+#include "Foundation/PDB_Memory.h"
+
+namespace
+{
+	// the IPI stream always resides at index 4
+	static constexpr const uint32_t IPIStreamIndex = 4u;
+}
+
+
+// ------------------------------------------------------------------------------------------------
+// ------------------------------------------------------------------------------------------------
+PDB::IPIStream::IPIStream(void) PDB_NO_EXCEPT
+	: m_header()
+	, m_stream()
+	, m_records(nullptr)
+	, m_recordCount(0u)
+{
+}
+
+
+// ------------------------------------------------------------------------------------------------
+// ------------------------------------------------------------------------------------------------
+PDB::IPIStream::IPIStream(IPIStream&& other) PDB_NO_EXCEPT
+	: m_header(PDB_MOVE(other.m_header))
+	, m_stream(PDB_MOVE(other.m_stream))
+	, m_records(PDB_MOVE(other.m_records))
+	, m_recordCount(PDB_MOVE(other.m_recordCount))
+{
+	other.m_records = nullptr;
+	other.m_recordCount = 0u;
+}
+
+
+// ------------------------------------------------------------------------------------------------
+// ------------------------------------------------------------------------------------------------
+PDB::IPIStream& PDB::IPIStream::operator=(IPIStream&& other) PDB_NO_EXCEPT
+{
+	if (this != &other)
+	{
+		PDB_DELETE_ARRAY(m_records);
+
+		m_header = PDB_MOVE(other.m_header);
+		m_stream = PDB_MOVE(other.m_stream);
+		m_records = PDB_MOVE(other.m_records);
+		m_recordCount = PDB_MOVE(other.m_recordCount);
+
+		other.m_records = nullptr;
+		other.m_recordCount = 0u;
+	}
+
+	return *this;
+}
+
+
+// ------------------------------------------------------------------------------------------------
+// ------------------------------------------------------------------------------------------------
+PDB::IPIStream::IPIStream(const RawFile& file, const IPI::StreamHeader& header) PDB_NO_EXCEPT
+	: m_header(header)
+	, m_stream(file.CreateMSFStream<CoalescedMSFStream>(IPIStreamIndex))
+	, m_records(nullptr)
+	, m_recordCount(GetLastTypeIndex() - GetFirstTypeIndex())
+{
+	// types in the IPI stream are accessed by their index from other streams.
+	// however, the index is not stored with types in the IPI stream directly, but has to be built while walking the stream.
+	// similarly, because types are variable-length records, there are no direct offsets to access individual types.
+	// we therefore walk the IPI stream once, and store pointers to the records for trivial O(N) array lookup by index later.
+	m_records = PDB_NEW_ARRAY(const CodeView::IPI::Record*, m_recordCount);
+
+	// ignore the stream's header
+	size_t offset = sizeof(IPI::StreamHeader);
+
+	// parse the CodeView records
+	uint32_t typeIndex = 0u;
+	while (offset < m_stream.GetSize())
+	{
+		// https://llvm.org/docs/PDB/CodeViewTypes.html
+		const CodeView::IPI::Record* record = m_stream.GetDataAtOffset<const CodeView::IPI::Record>(offset);
+		const uint32_t recordSize = GetCodeViewRecordSize(record);
+		m_records[typeIndex] = record;
+
+		// position the stream offset at the next record
+		offset += sizeof(CodeView::IPI::RecordHeader) + recordSize;
+
+		++typeIndex;
+	}
+}
+
+
+// ------------------------------------------------------------------------------------------------
+// ------------------------------------------------------------------------------------------------
+PDB::IPIStream::~IPIStream(void) PDB_NO_EXCEPT
+{
+	PDB_DELETE_ARRAY(m_records);
+}
+
+
+// ------------------------------------------------------------------------------------------------
+// ------------------------------------------------------------------------------------------------
+PDB_NO_DISCARD PDB::ErrorCode PDB::HasValidIPIStream(const RawFile& file) PDB_NO_EXCEPT
+{
+	const PDB::InfoStream infoStream(file);
+	if (!infoStream.HasIPIStream())
+	{
+		return ErrorCode::InvalidStream;
+	}
+
+	DirectMSFStream stream = file.CreateMSFStream<DirectMSFStream>(IPIStreamIndex);
+	if (stream.GetSize() < sizeof(IPI::StreamHeader))
+	{
+		return ErrorCode::InvalidStream;
+	}
+
+	const IPI::StreamHeader header = stream.ReadAtOffset<IPI::StreamHeader>(0u);
+	if (header.version != IPI::StreamHeader::Version::V80)
+	{
+		return ErrorCode::UnknownVersion;
+	}
+
+	return ErrorCode::Success;
+}
+
+
+// ------------------------------------------------------------------------------------------------
+// ------------------------------------------------------------------------------------------------
+PDB_NO_DISCARD PDB::IPIStream PDB::CreateIPIStream(const RawFile& file) PDB_NO_EXCEPT
+{
+	DirectMSFStream stream = file.CreateMSFStream<DirectMSFStream>(IPIStreamIndex);
+
+	const IPI::StreamHeader header = stream.ReadAtOffset<IPI::StreamHeader>(0u);
+	return IPIStream { file, header };
+}