Harden attestation payload parsing

[leopoldjoy]

Summary

• require _parseAttestation to consume the full outer payload map
• reject trailing bytes after definite-map entries or after an indefinite-map break marker
• add regression tests for both malformed payload shapes

Testing

• forge fmt --check src test
• forge test --match-contract NitroValidatorIndefiniteLengthTest -vvv
• forge test
• forge build --sizes