Fix graceful handling of malformed RFC 9421 sig

Improves error handling in HTTP signature creation and verification to
prevent 500 Internal Server Error responses when encountering malformed
RFC 9421 signatures. The verification process now gracefully handles
signature base creation failures and continues processing instead of
crashing.

Changes:

- Added try-catch blocks around createRfc9421SignatureBase calls
- Enhanced error messages for signature creation failures
- Added comprehensive test cases for error handling scenarios

Co-Authored-By: Claude <noreply@anthropic.com>