Log Loading & Feature Calculation Benchmark

[smly]

Measure the pipeline speed from game log loading through Observation encoding (feature calculation).

• Create Rust Criterion benchmark (benches/feature_bench.rs)
• Measure MJAI log parsing speed
• Measure Observation encoding throughput (encode.rs)
• Measure Sequence Feature calculation speed (sequence_features.rs)
• Measure Python-side data loader speed (pytest-benchmark)

Optional:

• Record baselines and enable CI regression detection