Run reload in a background thread to keep the server responsive

On large Rails apps (e.g., Bourgeois), reload takes 10-20 seconds.
During that time, the server can't process any other requests (model
info, route info, associations), causing the editor to freeze.

Run reload in a background thread and respond immediately. If another
reload arrives while one is in progress, skip it — the running reload
will pick up all file changes. This prevents N rapid saves from causing
N sequential 20-second reloads.

Trade-off: DSL generation may run against slightly stale state if it
starts before reload finishes. This is mitigated by the "don't delete
RBI" fix in Tapioca which preserves existing RBIs for missing constants.

Related: Shopify/team-ruby-dx#1734

Author: KaanOzkan

lib/ruby_lsp/ruby_lsp_rails/server.rb

@@ -320,15 +320,19 @@ def execute(request, params)
             send_result(run_migrations)
           end
         when "reload"
-          with_progress("rails-reload", "Reloading Ruby LSP Rails instance") do
-            begin
-              ::Rails.application.reloader.reload!
-              send_result({ success: true })
-            rescue StandardError => e
-              log_message(
-                "Request reload failed with #{e.class}:\n#{e.full_message(highlight: false)}",
-              )
-              send_result({ success: false })
+          # Respond immediately so callers are not blocked while the app reloads.
+          # Reload runs in a background thread to keep the server responsive to
+          # other requests (model, route, association, etc.).
+          # If a reload is already in progress, skip this one — the running reload
+          # will pick up all file changes.
+          if @reload_thread&.alive?
+            send_result({ success: true, skipped: true })
+          else
+            send_result({ success: true })
+            @reload_thread = Thread.new do
+              with_notification_error_handling("reload") do
+                ::Rails.application.reloader.reload!
+              end
             end
           end
         when "route_location"