Add connected? method to runner client (#565)

Add a `connected?` method to `RunnerClient`, so that we can make checks without having to use `is_a?`.

I also made `send_notification` and `make_request` private. They were not supposed to be public in the first place.

lib/ruby_lsp/ruby_lsp_rails/runner_client.rb

@@ -273,6 +273,13 @@ def stopped?
         [@stdin, @stdout, @stderr].all?(&:closed?) && !@wait_thread.alive?
       end
 
+      sig { returns(T::Boolean) }
+      def connected?
+        true
+      end
+
+      private
+
       sig do
         params(
           request: String,
@@ -288,8 +295,6 @@ def make_request(request, **params)
       sig { params(request: String, params: T.untyped).void }
       def send_notification(request, **params) = send_message(request, **params)
 
-      private
-
       sig { overridable.params(request: String, params: T.untyped).void }
       def send_message(request, **params)
         message = { method: request }
@@ -398,6 +403,11 @@ def rails_root
         Dir.pwd
       end
 
+      sig { returns(T::Boolean) }
+      def connected?
+        false
+      end
+
       private
 
       sig { params(message: ::String, type: ::Integer).void }