chore: fix all clippy warnings and improve code quality

[yslpn]

This PR addresses all clippy warnings in the codebase, making it more idiomatic Rust while maintaining all existing functionality.

Changes made:

• Documentation: Updated CONTRIBUTING.md with code quality guidelines
• CI Integration: Added clippy checks to GitHub Actions
• Code Quality: Fixed all clippy warnings (70+ issues)

Benefits:

• Enforced code quality standards in CI
• More idiomatic and readable Rust code
• Better code maintainability

Testing:

• All tests pass: cargo test
• No clippy warnings: cargo clippy --all-targets --all-features
• No functional changes, only code style improvements

[timofei-iatsenko]

LGTM