Add an interface for servers

[sagikazarmark]

Preflight Checklist

• I have searched the issue tracker for an issue that matches the one I want to file, without success.

Problem Description

#86 introduced custom server path prefixes as defined by the v7 specification.

It also introduced a new method called getPathPrefix, replacing the PATH_PREFIX constant as a better alternative for registering servers in a router.

With the introduction of this method, the signature of \Twirp\Server::registerServer becomes somewhat redundant:

public function registerServer(string $prefix, RequestHandlerInterface $server): void

(Now that I think of it: it was somewhat redundant before too because of the PATH_PREFIX constant)

Proposed Solution

Simplify the definition of registerServer:

public function registerServer(RequestHandlerInterface $server): void

This is probably not enough thought as the RequestHandlerInterface itself doesn't implement getPathPrefix, so we need a custom interface (see #88):

public function registerServer(Server $server): void

Alternatives Considered

Make the $prefix parameter optional and try to call getPathPrefix if it exists as a method, but sadly there is no way (other than reflection) to ensure that the method accepts no parameters and returns a string.

Additional Information

No response