* test: add comprehensive unit tests for Context.File() method
- Add TestContextFile with multiple test scenarios in context_test.go
- Add simplified tests in context_file_test.go
- Cover file serving, 404 handling, directory access, HEAD requests, and Range requests
- All tests pass successfully
* fix: resolve gci formatting issues in test files
* fix: correct test file paths and add test file to gin directory
* move test_file.txt to testdata directory as suggested by maintainer
* fix: update test file paths to use testdata directory
* Sleep for one millisecond in the handler because the `Latency` will return `0s` sometimes and the test will fail
* The `TCPListener.File` is not supported by windows, it is unimplemented now
* Remove the `LF` in the `testdata/template/raw.tmpl`, because if set the git config `core.autocrlf=true`, will append `CR` to the raw.tmpl automatically, then test is failed on Windows
