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, 69 insertions, 0 deletions

diff --git a/thirdparty/tourist/foundation/src/allocator.cpp b/thirdparty/tourist/foundation/src/allocator.cpp
new file mode 100644
index 000000000..c6f021ad2
--- /dev/null
+++ b/thirdparty/tourist/foundation/src/allocator.cpp
@@ -0,0 +1,69 @@
+#include <foundation/buffer.h>
+#include <foundation/malloc.h>
+
+#include "slab.h"
+
+//------------------------------------------------------------------------------
+Allocator::~Allocator()
+{
+    if (_slab != nullptr)
+        _slab->dec_ref();
+}
+
+//------------------------------------------------------------------------------
+MutableBuffer Allocator::create_buffer(uint32 size)
+{
+    auto create_slab = [this] (uint32 slab_size) {
+        auto* slab = tt_malloc<Slab>(slab_size + sizeof(Slab));
+        slab->_allocator = this;
+        slab->_size = slab_size;
+        slab->_refs.store_relaxed(0);
+        return slab;
+    };
+
+    enum {
+        PACKET_PAGE_SIZE    = 4 << 10,
+        PACKET_SLAB_SIZE    = 1 << 20,
+        PACKET_ALIGN        = 32 - 1,
+    };
+
+    if (size > PACKET_PAGE_SIZE)
+    {
+        Slab* slab = create_slab(size);
+        return MutableBuffer(slab, size, 0);
+    }
+
+    uint32 alloc_size = (size + PACKET_ALIGN) & ~PACKET_ALIGN;
+
+    UniqueLock _(_lock);
+
+    if (alloc_size > _slab_free && _slab != nullptr)
+    {
+        _slab->dec_ref();
+        _slab = nullptr;
+    }
+
+    if (_slab == nullptr)
+    {
+        _slab_free = PACKET_SLAB_SIZE;
+        _slab = create_slab(_slab_free);
+        _slab->inc_ref();
+    }
+
+    uint32 offset = PACKET_SLAB_SIZE - _slab_free;
+    _slab_free -= alloc_size;
+    return MutableBuffer(_slab, size, offset);
+}
+
+//------------------------------------------------------------------------------
+void Allocator::free_slab(Slab* slab)
+{
+    tt_free(slab);
+}
+
+//------------------------------------------------------------------------------
+Allocator& Allocator::get_from(Buffer& buffer)      { return get_from(buffer._slab); }
+Allocator& Allocator::get_from(BufferRef& ref)      { return get_from(ref.get_slab()); }
+Allocator& Allocator::get_from(BufferStream& stream){ return get_from(stream.get_slab()); }
+Allocator& Allocator::get_from(Pointer& pointer)    { return get_from(pointer.get_slab()); }
+Allocator& Allocator::get_from(const Slab* slab)    { return slab->get_allocator(); }