- Adjusted indentation and line breaks for structs, functions, and method calls to comply with Rust formatting standards.
- Improved error message formatting and consistency across `PkgTreeError` instances.
- Restructured long function arguments and chained calls for clarity and maintainability.
- Simplified conditional statements and loops for better readability.
- No functional changes introduced.
- Introduced caching headers (`Cache-Control`, `ETag`, `Last-Modified`) for file responses to improve client-side caching.
- Added HTTP admin routes for health check and authentication validation.
- Made `cache_max_age` configurable via server configuration with a default of 3600 seconds.
- Enhanced file handler with metadata-based `Last-Modified` computation.
- Updated integration tests to cover new functionality and ensure correctness.
