message: feat(server): give `Server::local_addr` a more general type
  Allows `local_addr` to work for any executor type, rather than just the default `Exec`. The
  underlying `SpawnAll::local_addr()` is already similarly general, so no other changes are needed
  other than adding the extra type parameter to the `impl`.
diff: @@ -134,7 +134,7 @@ impl Server<AddrIncoming, ()> {
  }
  #[cfg(feature = "tcp")]
  -impl<S> Server<AddrIncoming, S> {
  +impl<S, E> Server<AddrIncoming, S, E> {
  /// Returns the local address that this server is bound to.
  pub fn local_addr(&self) -> SocketAddr {
  self.spawn_all.local_addr()
  