feat: make MethodWeights cheap clone

[yjhmelody]

See

        // This state is cloned for every connection
        // all these types based on Arcs and it should
        // be relatively cheap to clone them.
        //
        // Make sure that nothing expensive is cloned here
        // when doing this or use an `Arc`.
        #[derive(Clone)]
        struct PerConnection<RpcMiddleware, HttpMiddleware> {
            methods: Methods,
            stop_handle: StopHandle,
            rpc_metrics: RpcMetrics,
            svc_builder: TowerServiceBuilder<RpcMiddleware, HttpMiddleware>,
            rate_limit_builder: Option<Arc<RateLimitBuilder>>,
            rpc_method_weights: MethodWeights,
        }