render3d: cut-out padding on every core - tex_dilate's rows per pass through Job.parallel_for, bytes unchanged

Within a pass a row writes only its own still-masked texels and reads only neighbours already let go,
which no row writes that pass, so the result is the single-threaded one. The worker takes a DilateJob
of plain buffers and allocates nothing. tex_dilate_bytes (safe_api) and examples/rendering/dilate.ludic,
which checks it against the old loop on RGB and RGBA atlases of sizes that do not divide (DILATE OK).

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

changes/dilate-parallel.md

@@ -0,0 +1,8 @@
+bump: patch
+type: performance
+**Cut-out edge padding runs on every core.** `tex_dilate`'s passes hand their rows, sixteen at a time, to
+`Job.parallel_for`: within a pass a row writes only its own still-masked texels and reads only
+neighbours the mask already let go, so the bytes are the ones the single-threaded loop made. The worker
+is handed plain buffers in a `DilateJob` and makes nothing. `tex_dilate_bytes` is the slice-taking
+form (safe_api.ludic), and `examples/rendering/dilate.ludic` holds the result against the old loop
+(prints DILATE OK). It was 206 ms of the main thread in a Maroon Lake boot.