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, 94 insertions, 0 deletions

diff --git a/src/zencore/intmath.cpp b/src/zencore/intmath.cpp
index fedf76edc..b460b5b78 100644
--- a/src/zencore/intmath.cpp
+++ b/src/zencore/intmath.cpp
@@ -7,6 +7,43 @@
 
 namespace zen {
 
+ReciprocalU64::ReciprocalU64(uint64_t Divisor)
+{
+	if (Divisor <= 1)
+	{
+		Mul	  = 0;	// Sentinel — Divide() returns Value directly.
+		Shift = 0;
+		return;
+	}
+
+	// m = ceil(2^(64+s) / d).  Start with s = 0; bump s only if
+	// the quotient doesn't fit in 64 bits (happens when d is a
+	// power of two, since 2^64 / 2^k = 2^(64-k) exactly and the
+	// +1 for ceil can overflow to zero).
+	for (uint32_t S = 0; S < 64; ++S)
+	{
+#if ZEN_PLATFORM_WINDOWS
+		uint64_t Remainder = 0;
+		uint64_t Quotient  = _udiv128(uint64_t(1) << S, 0, Divisor, &Remainder);
+		uint64_t M		   = Quotient + (Remainder ? 1 : 0);  // ceil
+#else
+		unsigned __int128 Num		= (unsigned __int128)(uint64_t(1) << S) << 64;
+		uint64_t		  Quotient	= uint64_t(Num / Divisor);
+		uint64_t		  Remainder = uint64_t(Num % Divisor);
+		uint64_t		  M			= Quotient + (Remainder ? 1 : 0);
+#endif
+		if (M != 0)
+		{
+			Mul	  = M;
+			Shift = S;
+			return;
+		}
+	}
+	// Unreachable for any Divisor > 1.
+	Mul	  = 0;
+	Shift = 0;
+}
+
 //////////////////////////////////////////////////////////////////////////
 //
 // Testing related code follows...
@@ -68,6 +105,63 @@ TEST_CASE("intmath")
 	CHECK(ByteSwap(uint64_t(0x214d'6172'7469'6e21ull)) == 0x216e'6974'7261'4d21ull);
 }
 
+TEST_CASE("ReciprocalU64 matches integer division")
+{
+	uint64_t Divisors[] = {1, 2, 3, 4, 5, 7, 10, 100, 1000, 3000, 3579};
+
+	for (uint64_t D : Divisors)
+	{
+		ReciprocalU64 R(D);
+
+		uint64_t TestValues[] = {
+			0,
+			1,
+			D - 1,
+			D,
+			D + 1,
+			D * 2,
+			D * 2 + 1,
+			1'000'000,
+			10'000'000,
+			100'000'000,
+			1'000'000'000ULL,
+			10'000'000'000ULL,
+			100'000'000'000ULL,
+			1'000'000'000'000ULL,
+			uint64_t(~0u),
+		};
+
+		for (uint64_t V : TestValues)
+		{
+			uint32_t Expected = uint32_t(V / D);
+			uint32_t Got	  = R.Divide(V);
+			CHECK_MESSAGE(Got == Expected, "V=", V, " D=", D, " expected=", Expected, " got=", Got);
+		}
+	}
+}
+
+TEST_CASE("ReciprocalU64 rounding division")
+{
+	// Verify the rounding pattern used in AbsorbBatch: (Cycle + half) / d
+	uint64_t Divisors[] = {3, 4, 5, 10, 3579};
+
+	for (uint64_t D : Divisors)
+	{
+		ReciprocalU64 R(D);
+		uint64_t	  Half = D >> 1;
+
+		uint64_t TestCycles[] = {0, 1, 100, 999'999, 1'000'000, 99'999'999, 1'000'000'000ULL, 50'000'000'000ULL};
+
+		for (uint64_t Cycle : TestCycles)
+		{
+			uint64_t Rounded  = Cycle + Half;
+			uint32_t Expected = uint32_t(Rounded / D);
+			uint32_t Got	  = R.Divide(Rounded);
+			CHECK_MESSAGE(Got == Expected, "Cycle=", Cycle, " D=", D, " expected=", Expected, " got=", Got);
+		}
+	}
+}
+
 TEST_SUITE_END();
 
 #endif