Do not resubscribe for Copilot logs events

Copilot sends multiple events about its LSP server readiness, not necessarily recreating the server from scratch (e.g. due to re-sign in action).
Avoid re-adding same log subscriptions on the same LSP server, which
causes panics.

crates/lsp/src/lsp.rs

@@ -605,6 +605,10 @@ impl LanguageServer {
         self.notification_handlers.lock().remove(T::METHOD);
     }
 
+    pub fn has_notification_handler<T: notification::Notification>(&self) -> bool {
+        self.notification_handlers.lock().contains_key(T::METHOD)
+    }
+
     #[must_use]
     pub fn on_custom_notification<Params, F>(&self, method: &'static str, mut f: F) -> Subscription
     where