feat: add opt-in 64-bit polygon references

[xsploit]

What

Adds an opt-in DT_POLYREF64 build mode to the WASM package and teaches the high-level core API to support either the existing 32-bit number references or 64-bit bigint references.

The default build and published ABI remain 32-bit.

Why

Large fine-grained tiled navmeshes can exhaust the 32-bit Detour polygon-reference bit budget even when JavaScript memory is otherwise sufficient. Recompiling Detour alone is not enough: polygon refs also cross the WebIDL/WASM boundary through scalar arguments, result refs, arrays, queries, Crowd targets, debug drawing, and direct-navmesh serialization.

Changes

• adds RECASTNAVIGATION_DT_POLYREF64 to the WASM CMake build;
• enables DT_POLYREF64 and Emscripten WASM_BIGINT together;
• generates the appropriate 32-bit or 64-bit WebIDL scalar/ref/array surface;
• exports a high-level PolyRef = number | bigint API with signed/unsigned normalization at the raw WASM boundary;
• updates navmesh, query, Crowd, Detour, and debug-drawer ref paths;
• gives 64-bit direct-navmesh serialization a distinct version so ABI-mismatched data fails closed;
• keeps compressed TileCache data ABI-portable because it contains no polygon refs;
• adds a changeset and CI coverage for both ABIs.

Compatibility and packaging

• Existing consumers continue to receive the 32-bit build and number refs by default.
• A 64-bit artifact is currently an opt-in source build.
• webidl-dts-gen does not parse unsigned long long[], so publishing a separate prebuilt 64-bit raw WASM package will still require a BigInt-aware raw declaration generator or checked-in declarations. The high-level core wrapper uses a runtime structural shim and is tested against both builds.

Testing

On Windows with Emscripten, Git Bash, Node 22, and Yarn 4:

• normal package build: pass;
• normal yarn test: 5/5 Vitest tests plus both Node smoke examples pass;
• raw WASM CTest in 32-bit mode: pass;
• raw WASM CTest in 64-bit mode: pass;
• high-level core smoke in 32-bit mode: pass;
• high-level core smoke in 64-bit mode: pass;
• exact 64-bit values above 2^53, including the full unsigned 64-bit bit pattern: pass.

yarn test:polyrefs now builds and exercises both ABIs in CI. It also avoids capturing Yarn's temporary Node shim by using Emscripten's stable cross-compiling emulator for CTest.

Downstream full-world evidence

This work was developed while testing H1Emu's fine full-world TileCache. A downstream superset branch, with separate TileCache import/native-region fixes that are intentionally not bundled into this PR, successfully materialized 104,935 layers across 100,289 columns into a single 64-bit navmesh with zero add/build failures. It was then exercised by a 2,000-agent benchmark, a 100-player two-hour-equivalent Crowd/obstacle soak, an installed-server startup, and real-client navigation testing.

• H1Emu comparison: Streaming fine navmesh via an in-RAM TileCache (h1emu pipeline) QuentinGruber/h1z1-server#2840 (comment)
• Downstream architecture evidence: https://github.com/xsploit/h1z1-server/blob/feat/navigation-batch-crawler/docs/navigation-full-pop-architecture.md
• Superset experimental branch: https://github.com/xsploit/recast-navigation-js/tree/spike/dt-polyref64-h1emu

The TileCache import-safety fixes, native intermediate-region widening, and downstream H1Emu integration will be proposed separately so this PR remains focused on the polygon-reference ABI and core API.