Simplify handling of forwarded RPC methods

[ferranbt]

We handle three types of RPC calls:

• Direct fallback: sent only to fallback EL node (e.g., eth_getBlockByNumber)
• Stateful multiplex: manipulate and forward to both nodes (e.g., engine_*)
• Forward: same request to both nodes, no processing (e.g., eth_sendRawTransaction, miner_*)

With the recent addition of DA throttling, we've added several miner_ methods that just need forwarding (miner_setExtra, miner_setGasPrice, miner_setGasLimit, miner_setMaxDASize).

Each of these requires the same boilerplate server implementation just to forward requests:

impl<C> MinerApiServer for EthEngineApi<HttpClientWrapper<C>> {
    async fn set_gas_limit(&self, gas_price: U128) -> RpcResult<bool> {
        // Forward to builder
        let builder_client = self.builder_client.client.clone();
        tokio::spawn(async move {
            builder_client.set_gas_limit(gas_price).await
        });

        // Forward to L2
        self.l2_client.client.set_gas_limit(gas_price).await
    }
}

The proposal is to add a new list of FORWARD_METHODS to handle these simple forwarding cases automatically without requiring full server implementations.

[avalonche]

can't this already be achieved at the proxy layer?