perf(render): cache stable ray proxy identities

[Arbousier1]

Summary

• let unchanged active viewers reuse their stored Player without repeating session.onlinePlayer(viewerId)
• resolve a fresh session Player only when no active proxy exists, geometry/ownership changed, or the cached Player is offline
• preserve the original coordinator, proxy record, registry and allocation-sensitive object layouts
• add regression coverage proving unchanged regions perform one viewer lookup while reconnects switch to a fresh Player

Performance

Latest local protected-profile smoke comparison against origin/dev:

• 1 viewer: 407.2 ns/op -> 326.4 ns/op (~19.8% lower)
• 4 viewers: 963.9 ns/op -> 868.5 ns/op (~9.9% lower)
• 32 viewers: 5209.7 ns/op -> 4884.3 ns/op (~6.2% lower)
• 1-viewer allocation: 2312 B/op -> 2224 B/op (~3.8% lower)
• 4-viewer allocation: 5536 B/op -> 5568 B/op (~0.6% increase)
• 32-viewer allocation: 31400 B/op -> 31376 B/op (flat/slightly lower)

Two earlier protected runs exposed escape-analysis regressions from added cache fields. Commit ef9ec5e removes all layout-changing caches and leaves only the viewer-lookup fast path.

Test plan

• SparrowRayInteractionProxyCoordinatorTest
• unchanged-region viewer lookup count
• offline cached viewer reconnect coverage
• null-session TableRegionKeyCacheTest compatibility
• spotlessCheck
• full check assemble (709 tests, 7 skipped)
• local RayProxyCoordinatorBenchmark smoke A/B
• protected ray-proxy paired A/B gate for ef9ec5e
• Linux, Windows, and macOS CI for ef9ec5e

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