refactor(eio-client): improve transports type (#5188)

Related: #5187

Author: nayounsang

packages/engine.io-client/lib/socket.ts

@@ -85,7 +85,9 @@ export interface SocketOptions {
    *
    * @default ['polling','websocket', 'webtransport']
    */
-  transports?: string[] | TransportCtor[];
+  transports?:
+    | ("polling" | "websocket" | "webtransport" | string)[]
+    | TransportCtor[];
 
   /**
    * Whether all the transports should be tested, instead of just the first one.