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, 102 insertions, 0 deletions

diff --git a/thirdparty/raw_pdb/src/PDB_InfoStream.cpp b/thirdparty/raw_pdb/src/PDB_InfoStream.cpp
new file mode 100644
index 000000000..fa166000f
--- /dev/null
+++ b/thirdparty/raw_pdb/src/PDB_InfoStream.cpp
@@ -0,0 +1,102 @@
+// 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_InfoStream.h"
+#include "PDB_RawFile.h"
+#include "Foundation/PDB_CRT.h"
+
+namespace
+{
+	// the PDB info stream always resides at index 1
+	static constexpr const uint32_t InfoStreamIndex = 1u;
+}
+
+
+// ------------------------------------------------------------------------------------------------
+// ------------------------------------------------------------------------------------------------
+PDB::InfoStream::InfoStream(void) PDB_NO_EXCEPT
+	: m_stream()
+	, m_header(nullptr)
+	, m_namesStreamIndex(0)
+	, m_usesDebugFastlink(false)
+	, m_hasIPIStream(false)
+{
+}
+
+
+// ------------------------------------------------------------------------------------------------
+// ------------------------------------------------------------------------------------------------
+PDB::InfoStream::InfoStream(const RawFile& file) PDB_NO_EXCEPT
+	: m_stream(file.CreateMSFStream<CoalescedMSFStream>(InfoStreamIndex))
+	, m_header(m_stream.GetDataAtOffset<const Header>(0u))
+	, m_namesStreamIndex(0)
+	, m_usesDebugFastlink(false)
+	, m_hasIPIStream(false)
+{
+	// the info stream starts with the header, followed by the named stream map, followed by the feature codes
+	// https://llvm.org/docs/PDB/PdbStream.html#named-stream-map
+	size_t streamOffset = sizeof(Header);
+
+	const NamedStreamMap* namedStreamMap = m_stream.GetDataAtOffset<const NamedStreamMap>(streamOffset);
+	streamOffset += sizeof(NamedStreamMap) + namedStreamMap->length;
+
+	const SerializedHashTable::Header* hashTableHeader = m_stream.GetDataAtOffset<const SerializedHashTable::Header>(streamOffset);
+	streamOffset += sizeof(SerializedHashTable::Header);
+
+	const SerializedHashTable::BitVector* presentBitVector = m_stream.GetDataAtOffset<const SerializedHashTable::BitVector>(streamOffset);
+	streamOffset += sizeof(SerializedHashTable::BitVector) + sizeof(uint32_t) * presentBitVector->wordCount;
+
+	const SerializedHashTable::BitVector* deletedBitVector = m_stream.GetDataAtOffset<const SerializedHashTable::BitVector>(streamOffset);
+	streamOffset += sizeof(SerializedHashTable::BitVector) + sizeof(uint32_t) * deletedBitVector->wordCount;
+
+	// the hash table entries can be used to identify the indices of certain common streams like:
+	//	"/UDTSRCLINEUNDONE"
+	//	"/src/headerblock"
+	//	"/LinkInfo"
+	//	"/TMCache"
+	//	"/names"
+
+	const NamedStreamMap::HashTableEntry* namedStreamMapHashEntries = m_stream.GetDataAtOffset<const NamedStreamMap::HashTableEntry>(streamOffset);
+
+	// Find "/names" stream, used to look up filenames for lines.
+	for (uint32_t i = 0, size = hashTableHeader->size; i < size; ++i)
+	{
+		const NamedStreamMap::HashTableEntry& entry = namedStreamMapHashEntries[i];
+		const char* streamName = &namedStreamMap->stringTable[entry.stringTableOffset];
+
+		if (strcmp("/names", streamName) == 0)
+		{
+			m_namesStreamIndex = entry.streamIndex;
+		}
+	}
+
+	streamOffset += sizeof(NamedStreamMap::HashTableEntry) * hashTableHeader->size;
+
+	// read feature codes by consuming remaining bytes
+	// https://llvm.org/docs/PDB/PdbStream.html#pdb-feature-codes
+	const FeatureCode* featureCodes = m_stream.GetDataAtOffset<const FeatureCode>(streamOffset);
+	const size_t remainingBytes = m_stream.GetSize() - streamOffset;
+	const size_t count = remainingBytes / sizeof(FeatureCode);
+
+	for (size_t i=0u; i < count; ++i)
+	{
+		FeatureCode code = featureCodes[i];
+		if (code == PDB::FeatureCode::MinimalDebugInfo)
+		{
+			m_usesDebugFastlink = true;
+		}
+		else if (code == PDB::FeatureCode::VC110 || code == PDB::FeatureCode::VC140)
+		{
+			m_hasIPIStream = true;
+		}
+	}
+}
+
+
+// ------------------------------------------------------------------------------------------------
+// ------------------------------------------------------------------------------------------------
+PDB::NamesStream PDB::InfoStream::CreateNamesStream(const RawFile& file) const PDB_NO_EXCEPT
+{
+	return NamesStream(file, m_namesStreamIndex);
+}