Add protocol property to serve.d.ts (#25267)

packages/bun-types/serve.d.ts

@@ -1082,6 +1082,15 @@ declare module "bun" {
      */
     readonly hostname: string | undefined;
 
+    /**
+     * The protocol the server is listening on.
+     *
+     * - "http" for normal servers
+     * - "https" when TLS is enabled
+     * - null for unix sockets or when unavailable
+     */
+    readonly protocol: "http" | "https" | null;
+
     /**
      * Is the server running in development mode?
      *