[bug] Using route.Methods(...) more than once

**Describe the bug** Using `func (r *Route) Methods(methods ...string)` more than once for a single route results in a response with status code `405 Method Not Allowed` for this route. **Background** I tried to simplify the development of my web APIs, so I introduced some utility functions, with the relevant part essentially being:

func RegisterRoute(
    mux *mux.Router,
    path string,
    methods []string,
    handler func(http.ResponseWriter, *http.Request),
  ) {
    mux.HandleFunc(path, handler).Methods("OPTIONS").Methods(methods...)
  }

(`OPTIONS` is basically always required; `methods` as a slice because `PUT`, `PATCH` and even `POST` may point to the same handler) **Versions** go version go1.19 windows/amd64 > package version: run `git rev-parse HEAD` inside the repo -- what repo? I used go to get `[email protected]` **Steps to Reproduce** ([GitHub repo](https://github.com/edgy-sphere/debug-mux))

package main

import (
	"log"
	"net/http"

	"github.com/gorilla/mux"
)

func main() {
	mux := mux.NewRouter()
	mux.HandleFunc("/test", handler).Methods("PUT").Methods("PATCH")

	server := &http.Server{
		Addr: ":9710",
		Handler: mux,
	}

	err := server.ListenAndServe()
	if err != nil {
		log.Fatal(err)
	}
}

func handler(w http.ResponseWriter, r *http.Request) {
	w.WriteHeader(200)
}

**Expected behavior** Response with status code 200 (for the latter example). **Solutions?** Either: - Disallow using `Methods(...)` more than once, e.g. via changing field `routeConf.matchers` from type `[]matcher` to type `map[string]matcher`, where key `string` (or any other practical type) may be `"METHODS"`. - Force method matchers to be unique and to be merged if it already exists, e.g. as per above. - Change `func (r *Route) Match(req *http.Request, match *RouteMatch)` to not return `ErrMethodMismatch` if _any_ method does not match, i.e. if there are multiple method matchers. It has been not clear to me that using `Methods(...)` twice leads to this behaviour (hence this issue), so I would at least appreciate some kind of information at the function description in the source file -- although _I_ do know now. Also, I neither fully understand your intended design nor Git things like Pull Requests, so I am sorry if my provided solutions may very well be rather lacking.