fix(types): ensure compatibility with TypeScript < 4.5

"import { type ... }" was added in TypeScript 4.5.

Reference: https://devblogs.microsoft.com/typescript/announcing-typescript-4-5/

Related:

- https://github.com/socketio/socket.io-adapter/issues/86
- https://github.com/socketio/socket.io/issues/3891

lib/cluster-adapter.ts

@@ -1,9 +1,5 @@
-import {
-  Adapter,
-  type BroadcastFlags,
-  type BroadcastOptions,
-  type Room,
-} from "./index";
+import { Adapter } from "./index";
+import type { BroadcastFlags, BroadcastOptions, Room } from "./index";
 import { debug as debugModule } from "debug";
 import { randomBytes } from "crypto";