- Introduced IfNoneMatch middleware to handle ETag-based caching:
  - Supports safe HTTP methods (GET, HEAD).
  - Returns "304 Not Modified" for matching ETags.
  - Handles multiple ETags and restores original request methods.

- Added EtagManager for flexible ETag generation:
  - Default ETag generation uses MD5 hash.
  - Supports custom hash algorithms like SHA-256 via callbacks.

- Included test cases:
  - Validate default ETag generation.
  - Test custom callback logic for ETag creation.

This commit adds foundational support for ETag-based caching in the application.

…ware

- Merged `etag.set` and `etag.if-none-match` middlewares into a single `etag.handle` middleware.
- Simplified logic to reduce redundancy and improve maintainability.
- Ensured ETag validation (`If-None-Match`) and generation are handled in the same flow.
- Preserved compatibility with HEAD requests for consistency.

This refactor improves clarity, reduces potential misconfigurations, and keeps the ETag logic centralized.

…d tests

- Created tests for the new `HandleEtag` middleware:
  - Validates ETag generation and correctness.
  - Tests responses for both matching and non-matching `If-None-Match` headers.
  - Ensures proper handling of weak ETags (`W/`).
- Removed old tests for `SetEtag` and `IfNoneMatch` middlewares as they are no longer needed.

This commit improves test clarity and ensures the new ETag middleware behaves as expected.

- Added a test to validate ETag generation for user-specific routes using `etag:user`.
  - Simulates an authenticated user and verifies the ETag includes the user ID.

These tests ensure the ETag middleware behaves correctly for both user-specific and common routes.