optimized sql queries in SEP-10 Authentication

[Litezy]

Closes #734
Closes #735
Closes #736

Summary

Optimizes the SEP-10 Authentication module across three areas: SQL query performance, cryptographic signature verification, and error recovery — improving platform robustness, security integrity, and developer experience.

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Changes

1. SQL Query Optimization

• Optimized database queries in the SEP-10 authentication flow to reduce latency and improve throughput
• Added appropriate indexes to support authentication lookup patterns
• Eliminated N+1 query patterns and redundant database round-trips
• Ensured all queries use parameterized inputs to prevent SQL injection

2. Cryptographic Signature Verification

• Added cryptographic signature verification to the SEP-10 authentication handshake
• Validates challenge transaction signatures against the client's registered public key before issuing tokens
• Rejects malformed, expired, or tampered signatures with descriptive error codes
• Follows SEP-10 specification requirements for signature verification flow

3. Error Recovery

• Improved error handling across the SEP-10 authentication lifecycle
• Added structured error responses with consistent error codes for all failure paths
• Implemented graceful recovery for transient failures (network timeouts, DB unavailability)
• Ensured partial failures do not leave authentication state in an inconsistent condition

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Security Notes

• All signature verification logic is tested against known-good and known-bad fixtures
• No secrets or private keys are logged at any verbosity level
• Error messages exposed to clients are sanitized — internal details stay server-side

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Testing

• Full test coverage added for all new logic
• Unit tests cover SQL query correctness, signature verification edge cases, and error recovery paths
• Existing test suite passes with no regressions

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