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, 84 insertions, 0 deletions

diff --git a/thirdparty/raw_pdb/src/PDB_DirectMSFStream.h b/thirdparty/raw_pdb/src/PDB_DirectMSFStream.h
new file mode 100644
index 000000000..70024592f
--- /dev/null
+++ b/thirdparty/raw_pdb/src/PDB_DirectMSFStream.h
@@ -0,0 +1,84 @@
+// 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)
+
+#pragma once
+
+#include "Foundation/PDB_Macros.h"
+
+
+// https://llvm.org/docs/PDB/index.html#the-msf-container
+// https://llvm.org/docs/PDB/MsfFile.html
+namespace PDB
+{
+	// provides direct access to the data of an MSF stream.
+	// inherently thread-safe, the stream doesn't carry any internal offset or similar.
+	// trivial to construct.
+	// slower individual reads, but pays off when not all data of a stream is needed.
+	class PDB_NO_DISCARD DirectMSFStream
+	{
+	public:
+		DirectMSFStream(void) PDB_NO_EXCEPT;
+		explicit DirectMSFStream(const void* data, uint32_t blockSize, const uint32_t* blockIndices, uint32_t streamSize) PDB_NO_EXCEPT;
+
+		PDB_DEFAULT_MOVE(DirectMSFStream);
+
+		// Reads a number of bytes from the stream.
+		void ReadAtOffset(void* destination, size_t size, size_t offset) const PDB_NO_EXCEPT;
+
+		// Reads from the stream.
+		template <typename T>
+		PDB_NO_DISCARD inline T ReadAtOffset(size_t offset) const PDB_NO_EXCEPT
+		{
+			T data;
+			ReadAtOffset(&data, sizeof(T), offset);
+			return data;
+		}
+
+		// Returns the block size of the stream.
+		PDB_NO_DISCARD inline uint32_t GetBlockSize(void) const PDB_NO_EXCEPT
+		{
+			return m_blockSize;
+		}
+
+		// Returns the size of the stream.
+		PDB_NO_DISCARD inline uint32_t GetSize(void) const PDB_NO_EXCEPT
+		{
+			return m_size;
+		}
+
+	private:
+		friend class CoalescedMSFStream;
+
+		struct IndexAndOffset
+		{
+			uint32_t index;
+			uint32_t offsetWithinBlock;
+		};
+
+		// Returns the block index and offset within the block that correspond to the given offset.
+		PDB_NO_DISCARD IndexAndOffset GetBlockIndexForOffset(uint32_t offset) const PDB_NO_EXCEPT;
+
+		// Returns the offset into the data that corresponds to the given indices and offset within a block.
+		PDB_NO_DISCARD size_t GetDataOffsetForIndexAndOffset(const IndexAndOffset& indexAndOffset) const PDB_NO_EXCEPT;
+
+		// Provides read-only access to the memory-mapped data.
+		PDB_NO_DISCARD inline const void* GetData(void) const PDB_NO_EXCEPT
+		{
+			return m_data;
+		}
+
+		// Provides read-only access to the block indices.
+		PDB_NO_DISCARD inline const uint32_t* GetBlockIndices(void) const PDB_NO_EXCEPT
+		{
+			return m_blockIndices;
+		}
+
+		const void* m_data;
+		const uint32_t* m_blockIndices;
+		uint32_t m_blockSize;
+		uint32_t m_size;
+		uint32_t m_blockSizeLog2;
+
+		PDB_DISABLE_COPY(DirectMSFStream);
+	};
+}