Ray: Balance movie tracing with dynamic chunks

Schedule ray-pool advancement in dynamic chunks of 32 slots to distribute frame-grouped active rays across workers while preserving stable endpoint destinations.

Add 1/4/16-thread lens-map equivalence coverage and document schedule comparisons with complete commands, input data and original logs. The 393-frame 64x36 production-source benchmark improves from 62.13 to 38.69 seconds with byte-identical PNGs and lens maps. Release and Debug test suites pass.

benchmarks/ray_pool_scheduling_2026-09-06/artifact-validation.json

@@ -0,0 +1,6 @@
+{
+  "successful_runs": 9,
+  "lens_map_sha256": "708a218eca26b9eac42cb4954b0dbd4dfe316cc55d4315d650cbc8ab7e616080",
+  "pngs_validated": 393,
+  "pngs_identical_before_after": 393
+}