ssh: Detect timeouts when server is unresponsive (#18808)

To detect connection timeouts we ping the remote server every X seconds
and attempt to reconnect if the server failed to respond.
Next up is showing some feedback in the UI to make this visible to the
user, and stop reconnecting after X amount of retries.

Release Notes:

- N/A

---------

Co-authored-by: Thorsten <thorsten@zed.dev>

crates/remote_server/src/headless_project.rs

@@ -113,6 +113,7 @@ impl HeadlessProject {
         client.add_request_handler(cx.weak_model(), Self::handle_list_remote_directory);
         client.add_request_handler(cx.weak_model(), Self::handle_check_file_exists);
         client.add_request_handler(cx.weak_model(), Self::handle_shutdown_remote_server);
+        client.add_request_handler(cx.weak_model(), Self::handle_ping);
 
         client.add_model_request_handler(Self::handle_add_worktree);
         client.add_model_request_handler(Self::handle_open_buffer_by_path);
@@ -354,4 +355,13 @@ impl HeadlessProject {
 
         Ok(proto::Ack {})
     }
+
+    pub async fn handle_ping(
+        _this: Model<Self>,
+        _envelope: TypedEnvelope<proto::Ping>,
+        _cx: AsyncAppContext,
+    ) -> Result<proto::Ack> {
+        log::debug!("Received ping from client");
+        Ok(proto::Ack {})
+    }
 }