Perf: Optimize scene snapshot materialization

[rian-be]

Summary

Optimize scene snapshot materialization by moving ordering, indexing, and edge cleanup into dedicated materializer while preserving current render state semantics.

Added

• Dedicated scene snapshot materializer in the rendering state layer to own node ordering, node lookup indexing, and edge remapping work
• Regression coverage for scene snapshot node ordering, node lookup, and invalid or duplicate edge remapping behavior
• Lightweight ordered node and remapped edge snapshot views to avoid unnecessary full buffer copies during materialization

Changed

• SceneSnapshot now uses a compact id-to-position lookup instead of duplicating full node snapshots in a second index
• Scene snapshot construction now routes through SceneSnapshotMaterializer instead of concentrating sorting, indexing, and edge cleanup inside the snapshot constructor
• Edge filtering and deduplication now run through explicit materialization logic instead of LINQ ordering and DistinctBy passes in the constructor
• Rendering benchmarks and fixtures now exercise the materializer path directly

Fixed

• Removed duplicated node snapshot indexing work from scene snapshot materialization
• Reduced unnecessary constructor side sorting, filtering, and edge dedup allocation in the hot path

Result

Scene snapshot materialization now does less repeated indexing and constructor work while preserving the same observable render state behavior.

At 100000 events:

• MaterializeSceneSnapshot: 110.26 ms -> 51.55 ms, 26.77 MB -> 3.85 MB

Testing

• dotnet test Tests/ChangeTrace.Tests.csproj --filter "FullyQualifiedName~ChangeTrace.Tests.Rendering.States"
• dotnet run -c Release --project Benchmarks/ChangeTrace.Benchmarks.csproj -- --filter "*SceneSnapshotComponentBenchmarks.MaterializeSceneSnapshot*"

Additional notes:

• The optimization is kept in one reviewable commit, with the materialization split moved into States/Scene while snapshot model types remain in the existing snapshot area.

Linked Issues

• Closes [Task]: Benchmark and optimize SceneSnapshot materialization performance #51

Checklist

• PR is focused and does not include unrelated cleanup
• Public API changes are documented
• Breaking changes are explicitly described
• New behavior follows existing project architecture
• I followed the Code of Conduct