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, 123 insertions, 0 deletions

diff --git a/src/zen/trace/timeline_query.cpp b/src/zen/trace/timeline_query.cpp
new file mode 100644
index 000000000..d90c79a29
--- /dev/null
+++ b/src/zen/trace/timeline_query.cpp
@@ -0,0 +1,123 @@
+// Copyright Epic Games, Inc. All Rights Reserved.
+
+#include "timeline_query.h"
+
+#include <algorithm>
+
+namespace zen::trace_detail {
+
+namespace {
+
+	// Pick the LOD level a given resolution should read from. Mirrors the
+	// historical selection in trace_viewer_service.cpp: resolution 0 reads the
+	// raw LOD 0; otherwise the smallest LOD whose ResolutionUs >= the request
+	// wins, falling back to the coarsest level if none qualify.
+	//
+	// Returned values: 0 == raw scopes (LOD 0), 1..kTimelineLodCount == DetailLevels[lod-1].
+	size_t SelectLodIndex(uint32_t ResolutionUs)
+	{
+		if (ResolutionUs == 0)
+		{
+			return 0;
+		}
+		for (size_t I = 0; I < kTimelineLodCount; ++I)
+		{
+			if (kTimelineLodResolutions[I] >= ResolutionUs)
+			{
+				return I + 1;
+			}
+		}
+		return kTimelineLodCount;
+	}
+
+	const eastl::vector<TimelineScope>& LodScopes(const ThreadTimeline& Timeline, size_t LodIndex)
+	{
+		if (LodIndex == 0)
+		{
+			return Timeline.Scopes;
+		}
+		return Timeline.DetailLevels[LodIndex - 1].Scopes;
+	}
+
+	void ExtractScopesInto(const ThreadTimeline& Timeline, const TimelineQueryRequest& Req, std::vector<TimelineScopeView>& Out)
+	{
+		const eastl::vector<TimelineScope>& Scopes = LodScopes(Timeline, SelectLodIndex(Req.ResolutionUs));
+
+		auto MidIt =
+			std::lower_bound(Scopes.begin(), Scopes.end(), Req.StartUs, [](const TimelineScope& S, uint32_t V) { return S.BeginUs < V; });
+
+		for (auto It = Scopes.begin(); It != MidIt; ++It)
+		{
+			if ((It->BeginUs + It->DurationUs) < Req.StartUs || It->DurationUs < Req.MinDurUs)
+			{
+				continue;
+			}
+			Out.push_back({It->BeginUs, It->DurationUs, It->NameId, It->Depth, It->MergeCount});
+		}
+		for (auto It = MidIt; It != Scopes.end(); ++It)
+		{
+			if (It->BeginUs > Req.EndUs)
+			{
+				break;
+			}
+			if (It->DurationUs < Req.MinDurUs)
+			{
+				continue;
+			}
+			Out.push_back({It->BeginUs, It->DurationUs, It->NameId, It->Depth, It->MergeCount});
+		}
+	}
+
+	const ThreadTimeline* FindThread(const TraceModel& Model, uint32_t ThreadId)
+	{
+		auto It = std::find_if(Model.Timelines.begin(), Model.Timelines.end(), [ThreadId](const ThreadTimeline& T) {
+			return T.ThreadId == ThreadId;
+		});
+		return (It != Model.Timelines.end()) ? &*It : nullptr;
+	}
+
+	class InMemoryTimelineQuery final : public TimelineQuery
+	{
+	public:
+		explicit InMemoryTimelineQuery(const TraceModel& Model) : m_Model(Model) {}
+
+		void QueryThread(uint32_t ThreadId, const TimelineQueryRequest& Req, std::vector<TimelineScopeView>& Out) const override
+		{
+			const ThreadTimeline* Timeline = FindThread(m_Model, ThreadId);
+			if (Timeline)
+			{
+				ExtractScopesInto(*Timeline, Req, Out);
+			}
+		}
+
+		void QueryBatch(std::span<const uint32_t> ThreadIds, const TimelineQueryRequest& Req, BatchResult& Out) const override
+		{
+			Out.Scopes.clear();
+			Out.Ranges.clear();
+			Out.Ranges.reserve(ThreadIds.size());
+
+			for (uint32_t ThreadId : ThreadIds)
+			{
+				const uint32_t		  Begin	   = uint32_t(Out.Scopes.size());
+				const ThreadTimeline* Timeline = FindThread(m_Model, ThreadId);
+				if (Timeline)
+				{
+					ExtractScopesInto(*Timeline, Req, Out.Scopes);
+				}
+				Out.Ranges.push_back({Begin, uint32_t(Out.Scopes.size())});
+			}
+		}
+
+	private:
+		const TraceModel& m_Model;
+	};
+
+}  // namespace
+
+std::unique_ptr<TimelineQuery>
+MakeInMemoryTimelineQuery(const TraceModel& Model)
+{
+	return std::make_unique<InMemoryTimelineQuery>(Model);
+}
+
+}  // namespace zen::trace_detail