fix(texture): keep coordinate UVs out of atlas regions

[snowyukitty]

Description

Numeric source-rectangle lookups currently create named regions, while addUVs() adds coordinate aliases for every frame. Cropped images and repeating patterns therefore change the same dictionary that animation consumers enumerate. Identical rectangles on different atlas pages can also reuse the previous page's UVs.

This separates numeric UV caching from named regions. Parsed frames seed the private numeric cache with their existing UV arrays; arbitrary rectangles are cached without registering frames. The last-lookup cache checks the active atlas dictionary and is invalidated when addUVs() replaces a rectangle. Both GPU pattern consumers now use numeric lookups. The batchers already receive UV values, so their interfaces stay the same.

Compatibility: getUVs(name) now throws a descriptive error for an unknown name. Use getUVs(x, y, width, height) instead of a coordinate string, or explicitly define a named region with addRegion(). Explicitly authored names containing commas still work.

13 new browser regressions cover dictionary purity, frame UV reuse, alternating crops, missing names, named-coordinate collisions, atlas page changes, replacement, intrinsic video dimensions, packed rotated/trimmed frames, and both GPU pattern consumers. Real WebGL pixel checks cover cropped images and repeating patterns; WebGPU's changed consumer is exercised with the real atlas and a recording batcher, rather than a WebGPU pixel test.

Validation

• pnpm lint
• pnpm build
• pnpm test — 7933 passed, 11 skipped
• pnpm -F @melonjs/matter-adapter test — 226 passed
• pnpm -F @melonjs/planck-adapter test — 221 passed
• pnpm -F @melonjs/debug-plugin test — 23 passed
• Focused texture/atlas suite: 81 passed. Applying the new regressions to the unmodified base gives 10 failures and 3 passes; the cropped/repeating pixel assertions already pass on the base, followed by the failing dictionary-mutation assertions.

A Chromium CPU microbenchmark interleaved the original and changed TextureAtlas.getUVs() implementations for 20 rounds of 1,000,000 lookups per workload after warm-up, alternating run order and checking equal UV checksums. Median milliseconds per round:

Workload	Base	Candidate
Same frame	3.4	7.8
Alternating 128 frames	141.6	61.7
Alternating 128 fractional crops	255.0	64.6

The same-frame path pays a few extra nanoseconds per lookup for the atlas check; alternating rectangles avoid string keys and region searches. These are lookup timings on one Chromium/Linux container, not an FPS measurement. Cache retention remains unchanged in principle: previously encountered rectangles stay cached for the atlas lifetime.

Type of change

• Bug fix

Checklist

• I have read the Contributing Guide
• pnpm lint passes
• pnpm test passes
• Regression tests cover the changes
• pnpm build succeeds

Related issues

Refs #1281. This addresses the remaining atlas lookup work on the current renderer, whose batchers already consume UVs directly.