[#549] Make attestation metrics internally consistent

[Baskarayelu]

Summary

• enforce bounded fee and drawdown inputs across single and batch attestation paths
• use checked arithmetic for fee aggregates and all attestation counters
• preserve atomic rollback when a metric update is rejected
• add deterministic consistency tests and contract metric documentation

Issue coverage

• Counters and scores stay within documented bounds
• Equivalent operation sequences produce equivalent totals
• Rejected records leave metrics and history unchanged
• Empty, single, mixed, repeated, maximum, and overflow histories are covered

Validation

• cargo +1.88.0 test -p attestation_engine metric_consistency_tests
• cargo +1.88.0 test -p attestation_engine --lib (56 passed)
• git diff --cached --check

Closes #549