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, 68 insertions, 0 deletions

diff --git a/thirdparty/raw_pdb/src/PDB_SourceFileStream.cpp b/thirdparty/raw_pdb/src/PDB_SourceFileStream.cpp
new file mode 100644
index 000000000..fc860f622
--- /dev/null
+++ b/thirdparty/raw_pdb/src/PDB_SourceFileStream.cpp
@@ -0,0 +1,68 @@
+// 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_SourceFileStream.h"
+
+
+// ------------------------------------------------------------------------------------------------
+// ------------------------------------------------------------------------------------------------
+PDB::SourceFileStream::SourceFileStream(void) PDB_NO_EXCEPT
+	: m_stream()
+	, m_moduleCount(0u)
+	, m_moduleIndices(nullptr)
+	, m_moduleFileCounts(nullptr)
+	, m_fileNameOffsets(nullptr)
+	, m_stringTable(nullptr)
+{
+}
+
+
+// ------------------------------------------------------------------------------------------------
+// ------------------------------------------------------------------------------------------------
+PDB::SourceFileStream::SourceFileStream(const DirectMSFStream& directStream, uint32_t size, uint32_t offset) PDB_NO_EXCEPT
+	: m_stream(directStream, size, offset)
+	, m_moduleCount(0u)
+	, m_moduleIndices(nullptr)
+	, m_moduleFileCounts(nullptr)
+	, m_fileNameOffsets(nullptr)
+	, m_stringTable(nullptr)
+{
+	// we are going to consume the whole source info sub-stream, so create a coalesced stream for faster read operations and direct access.
+	// the sub-stream has the following layout:
+	//	struct SourceInfoSubstream
+	//	{
+	//		uint16_t moduleCount;
+	//		uint16_t sourceFileCount;
+	//		uint16_t moduleIndices[moduleCount];
+	//		uint16_t moduleFileCounts[moduleCount];
+	//		uint32_t fileNameOffsets[realSourceFileCount];
+	//		char stringTable[][realSourceFileCount];
+	//	};
+	m_moduleCount = *m_stream.GetDataAtOffset<uint16_t>(0u);
+	size_t readOffset = sizeof(uint16_t);
+
+	// skip number of source files. this would only support 64k unique files and is no longer used.
+	// the number of source files is computed dynamically instead.
+	readOffset += sizeof(uint16_t);
+
+	// grab direct pointers into the stream data
+	m_moduleIndices = m_stream.GetDataAtOffset<uint16_t>(readOffset);
+	readOffset += sizeof(uint16_t) * m_moduleCount;
+
+	m_moduleFileCounts = m_stream.GetDataAtOffset<uint16_t>(readOffset);
+	readOffset += sizeof(uint16_t) * m_moduleCount;
+
+	// count the actual number of source files
+	size_t sourceFileCount = 0u;
+	for (unsigned int i = 0u; i < m_moduleCount; ++i)
+	{
+		sourceFileCount += m_moduleFileCounts[i];
+	}
+
+	m_fileNameOffsets = m_stream.GetDataAtOffset<uint32_t>(readOffset);
+	readOffset += sizeof(uint32_t) * sourceFileCount;
+
+	// grab a pointer into the string table
+	m_stringTable = m_stream.GetDataAtOffset<char>(readOffset);
+}