feat: update HTTP method parsing in patterns for Handle and HandleFunc

[angelofallars]

Resolves #899

Makes the Mux.HandleFunc method also support patterns that include an HTTP method. This is the behavior consistent with Go 1.22's net/http.ServeMux. Previously, only Mux.Handle supported HTTP method patterns according to #897 .

• Made Mux.HandleFunc call Mux.Method when a method pattern is detected.
• Refactored Mux.Handle to call Mux.Method instead. Error handling for unrecognized HTTP methods is still kept this way.
• Updated TestMuxHandlePatternValidation to also test Mux.HandleFunc.

[floleg]

Hi @angelofallars! Thanks for this improvement which will be very much appreciated.

Once merged, have you any idea when we can expect to have it shipped on a new release?

Thanks again, and have a great day!

[pkieltyka]

thanks @angelofallars