Errors for all RPC Requests (#5867)

* Return and error if peer has disconnected

* Report errors for rate limited requests

* Code improvement

* Bump rust version to 1.78

* Downgrade to 1.77

* Update beacon_node/lighthouse_network/src/service/mod.rs

Co-authored-by: João Oliveira <hello@jxs.pt>

* fix fmt

* Merge branch 'unstable' of https://github.com/sigp/lighthouse into rpc-peer-disconnect-error

* update lockfile

beacon_node/lighthouse_network/src/service/mod.rs

@@ -917,12 +917,23 @@ impl<AppReqId: ReqId, E: EthSpec> Network<AppReqId, E> {
     /* Eth2 RPC behaviour functions */
 
     /// Send a request to a peer over RPC.
-    pub fn send_request(&mut self, peer_id: PeerId, request_id: AppReqId, request: Request) {
+    pub fn send_request(
+        &mut self,
+        peer_id: PeerId,
+        request_id: AppReqId,
+        request: Request,
+    ) -> Result<(), (AppReqId, RPCError)> {
+        // Check if the peer is connected before sending an RPC request
+        if !self.swarm.is_connected(&peer_id) {
+            return Err((request_id, RPCError::Disconnected));
+        }
+
         self.eth2_rpc_mut().send_request(
             peer_id,
             RequestId::Application(request_id),
             request.into(),
-        )
+        );
+        Ok(())
     }
 
     /// Send a successful response to a peer over RPC.