* test(ginS): add comprehensive test coverage for ginS package
Improve test coverage for ginS package by adding 18 test functions covering HTTP methods, routing, middleware, static files, and templates.
* use http.Method* constants instead of raw strings in gins_test.go
* copyright updated in gins_test.go
---------
Co-authored-by: Bo-Yi Wu <appleboy.tw@gmail.com>
