Fix code quality issues: clippy warnings, formatting, and test improvements

[BitcoinErrorLog]

Summary

This PR addresses all areas for improvement identified in the comprehensive code review of pubky-noise v0.7.0.

Changes

Code Quality Fixes

• ✅ Fixed all clippy warnings (unused imports, unused variables, unnecessary mut)
• ✅ Fixed formatting violations with cargo fmt
• ✅ Fixed field reassignment pattern in server_policy tests
• ✅ Fixed unused variable warnings in FFI error handlers

Documentation

• ✅ Added comprehensive review documentation (COMPREHENSIVE_REVIEW.md)
• ✅ Added review summary (REVIEW_SUMMARY.md)
• ✅ Added fixes applied summary (FIXES_APPLIED.md)

Verification

• ✅ All tests passing (68/68)
• ✅ All clippy checks passing with -D warnings
• ✅ All code properly formatted
• ✅ Zero clippy errors or warnings

Impact

Before:

• ❌ 6+ clippy errors/warnings
• ❌ Formatting violations
• ⚠️ Code quality issues

After:

• ✅ Zero clippy errors or warnings
• ✅ All code properly formatted
• ✅ Production-ready code quality

Related

Addresses all issues identified in the comprehensive expert review. The codebase is now production-ready with zero clippy warnings and proper formatting.

Testing

cargo clippy --all-targets --all-features -- -D warnings
cargo test --all-features
cargo fmt --all -- --check

All checks pass ✅