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, 86 insertions, 0 deletions

diff --git a/thirdparty/raw_pdb/src/PDB_TPIStream.cpp b/thirdparty/raw_pdb/src/PDB_TPIStream.cpp
new file mode 100644
index 000000000..164195ecd
--- /dev/null
+++ b/thirdparty/raw_pdb/src/PDB_TPIStream.cpp
@@ -0,0 +1,86 @@
+#include "PDB_PCH.h"
+#include "PDB_TPIStream.h"
+#include "PDB_RawFile.h"
+#include "PDB_DirectMSFStream.h"
+#include "Foundation/PDB_Memory.h"
+
+namespace
+{
+	// the TPI stream always resides at index 2
+	static constexpr const uint32_t TPIStreamIndex = 2u;
+}
+
+
+// ------------------------------------------------------------------------------------------------
+// ------------------------------------------------------------------------------------------------
+PDB::TPIStream::TPIStream(void) PDB_NO_EXCEPT
+	: m_stream()
+	, m_header()
+	, m_recordCount(0u)
+{
+}
+
+
+// ------------------------------------------------------------------------------------------------
+// ------------------------------------------------------------------------------------------------
+PDB::TPIStream::TPIStream(TPIStream&& other) PDB_NO_EXCEPT
+	: m_stream(PDB_MOVE(other.m_stream))
+	, m_header(PDB_MOVE(other.m_header))
+	, m_recordCount(PDB_MOVE(other.m_recordCount))
+{
+	other.m_recordCount = 0u;
+}
+
+
+// ------------------------------------------------------------------------------------------------
+// ------------------------------------------------------------------------------------------------
+PDB::TPIStream& PDB::TPIStream::operator=(TPIStream&& other) PDB_NO_EXCEPT
+{
+	if (this != &other)
+	{
+		m_stream = PDB_MOVE(other.m_stream);
+		m_header = PDB_MOVE(other.m_header);
+		m_recordCount = PDB_MOVE(other.m_recordCount);
+
+		other.m_recordCount = 0u;
+	}
+
+	return *this;
+}
+
+
+// ------------------------------------------------------------------------------------------------
+// ------------------------------------------------------------------------------------------------
+PDB::TPIStream::TPIStream(const RawFile& file) PDB_NO_EXCEPT
+	: m_stream(file.CreateMSFStream<DirectMSFStream>(TPIStreamIndex)),
+	  m_header(m_stream.ReadAtOffset<TPI::StreamHeader>(0u)),
+	  m_recordCount(GetLastTypeIndex() - GetFirstTypeIndex())
+{
+}
+
+// ------------------------------------------------------------------------------------------------
+// ------------------------------------------------------------------------------------------------
+PDB_NO_DISCARD PDB::ErrorCode PDB::HasValidTPIStream(const RawFile& file) PDB_NO_EXCEPT
+{
+	DirectMSFStream stream = file.CreateMSFStream<DirectMSFStream>(TPIStreamIndex);
+	if (stream.GetSize() < sizeof(TPI::StreamHeader))
+	{
+		return ErrorCode::InvalidStream;
+	}
+
+	const TPI::StreamHeader header = stream.ReadAtOffset<TPI::StreamHeader>(0u);
+	if (header.version != TPI::StreamHeader::Version::V80)
+	{
+		return ErrorCode::UnknownVersion;
+	}
+
+	return ErrorCode::Success;
+}
+
+
+// ------------------------------------------------------------------------------------------------
+// ------------------------------------------------------------------------------------------------
+PDB_NO_DISCARD PDB::TPIStream PDB::CreateTPIStream(const RawFile& file) PDB_NO_EXCEPT
+{
+	return TPIStream { file };
+}