nav, physics: Recast's and Detour's memory counted (nav_heap_bytes / _peak / _allocs, a counted allocator registered at load, tile bytes staged from it); package tests that crossing the map and back holds the native bytes

The user's walk showed the footprint rising outside the Ludic heap. Jolt's bytes were already counted;
the navmesh's were not, so nothing could see them. Now:
- ludic.nav nav_heap_test: fifty crossings of a four-tile map by the resident index hold the tiles in and
  the native bytes to the first crossing's; a thousand crowd walkers in and out grow nothing; a reset
  gives back every byte the mesh took.
- ludic.physics cross_heap_test: a 1 km map of 64 m chunks kept to a ring round a player crossing
  corner to corner and back, each chunk a heightfield, twelve owned posts and six owned scaled hulls
  as the game makes them: six more crossings hold the bodies, the shapes and Jolt's bytes and peak
  exactly. (A post made as an offset of a cylinder, with only the offset owned, leaked the cylinder
  every time: the game's solid_pillar owns its cylinder directly.)

lib/macos-arm64 rebuilt; lib/windows-x64 needs native/build.sh run on the PC for the new exports.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

packages/ludic.nav/README.md

@@ -72,6 +72,12 @@ across the seams, a tile under water with no polygons, and the set saved and loa
 and the shim (`native/shim/nav_shim.cpp`) into `lib/<target>/` - the same script on the Mac and on
 the PC (Git Bash, the LLVM installer's clang). `native/LICENSE-recastnavigation` ships with it.
 
+Every byte Recast and Detour allocate - the tiles in, the queries, the crowds - goes through a counted
+allocator registered when the library loads (`native/shim/nav_alloc.inl`, as ludic.physics counts
+Jolt's): `nav_heap_bytes()`, `nav_heap_peak()` and `nav_heap_allocs()`. A tile's bytes are staged from
+it too, since Detour frees them with the tile. `tests/nav_heap_test` holds fifty crossings of the map
+and a thousand crowd walkers to the bytes of the first, and a reset to the bytes before the mesh.
+
 ## Crowds (phase 18)
 
 `nav_crowd_start(kind, max, max_radius)` puts a DetourCrowd on a kind's mesh, with the mesh's tastes as