test: Improve test coverage and fix compiler warnings

[K-NRS]

Summary

This PR significantly improves the test suite and cleans up all compiler warnings in the codebase.

Changes

🧪 Test Coverage Improvements

• Added 40+ unit tests for PTY modules covering:
  • Client operations and terminal size handling
  • Socket communication and NDS command parsing
  • Terminal refresh sequences
  • IO handler and scrollback buffer
  • Session switcher functionality
• Added comprehensive integration tests for session lifecycle:
  • Session creation, listing, renaming, and termination
  • Partial ID/name matching
  • Multiple session management
  • History and cleanup operations
• Increased total test count from 11 to 53+ tests
• Added extensive edge case testing (empty inputs, broken pipes, zero dimensions, etc.)

🔧 Compiler Warning Fixes

• Fixed all 10 compiler warnings by adding appropriate annotations
• Preserved public API functions that may be used by external consumers
• Properly handled unused private fields in structs

🎨 Code Quality

• Added pre-commit hook for automatic rustfmt checking
• Ensures consistent code formatting across the project
• Prevents future CI failures due to formatting issues

Testing

All tests pass successfully:

test result: ok. 53 passed; 0 failed; 0 ignored

CI Status

• ✅ All compiler warnings resolved
• ✅ Rustfmt check passes
• ✅ Test suite comprehensive and passing