Feat: BenchmarkDotNet suites for render and player pipelines

[rian-be]

Introduce dedicated BenchmarkDotNet benchmarks for CPU side render pipeline and player performance analysis.

Added

Benchmark project
- Adds Benchmarks/ChangeTrace.Benchmarks.csproj
- Adds BenchmarkDotNet dependency
- References production ChangeTrace code from separate benchmark project
- Keeps benchmark code excluded from normal application runtime

Render pipeline benchmarks
- Adds render event translation benchmark
- Adds render state assembly benchmark
- Adds scene snapshot assembly benchmark
- Adds scene frame update benchmark
- Adds render frame submission benchmark
- Adds CPU side GPU buffer data preparation benchmark
- Adds hive layout step and convergence benchmarks

Player benchmarks
- Adds event cursor seek and drain benchmarks
- Adds seekable timeline benchmarks
- Adds timeline stepper traversal benchmark
- Adds timeline player factory benchmark

Benchmark fixtures
- Adds deterministic render benchmark fixture
- Generates synthetic render scenes for 1k, 10k and 100k event scenarios
- Adds deterministic player timeline fixture
- Avoids OpenTK window creation and real GPU access

Documentation and tooling
- Adds benchmark README with local run commands
- Adds task benchmark command for render pipeline benchmarks
- Enables memory allocation diagnostics
- Documents BenchmarkDotNet report output and runtime notes

Result

These changes provide repeatable CPU side performance baselines for render translation, layout, snapshot assembly, GPU data preparation and player playback paths before deeper optimization work.