perf: cache attestation health metrics incrementally

[dangelo352]

Summary

• update attestation_engine HealthMetrics from each new attestation instead of reducing full history on every write
• mark updater-written caches so get_health_metrics/calculate_compliance_score can use O(1) cached aggregate fields while legacy/manual caches still fall back to full recomputation
• add cached-vs-full-recompute equivalence coverage for mixed fee/drawdown attestations
• document the before/after cost shape in benchmarks/results

Fixes #496.

Tests

• CARGO_TARGET_DIR=/tmp/commitlabs-attestation-cache-target cargo test -p attestation_engine health_metrics -- --nocapture
• CARGO_TARGET_DIR=/tmp/commitlabs-attestation-cache-target cargo test -p attestation_engine incremental_health_metrics -- --nocapture
• CARGO_TARGET_DIR=/tmp/commitlabs-attestation-cache-target cargo test -p attestation_engine record_fees -- --nocapture
• CARGO_TARGET_DIR=/tmp/commitlabs-attestation-cache-target cargo test -p attestation_engine record_drawdown -- --nocapture
• git diff --check