fix: properly parse the CONNECT packet in v2 compatibility mode

In Socket.IO v2, the Socket query option was appended to the namespace
in the CONNECT packet:

{
  type: 0,
  nsp: "/my-namespace?abc=123"
}

Note: the "query" option on the client-side (v2) will be found in the
"auth" attribute on the server-side:

```
// client-side
const socket = io("/nsp1", {
  query: {
    abc: 123
  }
});
socket.query = { abc: 456 };

// server-side
const io = require("socket.io")(httpServer, {
  allowEIO3: true // enable compatibility mode
});

io.of("/nsp1").on("connection", (socket) => {
  console.log(socket.handshake.auth); // { abc: 456 } (the Socket query)
  console.log(socket.handshake.query.abc); // 123 (the Manager query)
});

More information here: https://socket.io/docs/v3/migrating-from-2-x-to-3-0/#Add-a-clear-distinction-between-the-Manager-query-option-and-the-Socket-query-option

Related: #3791

lib/client.ts

@@ -1,5 +1,6 @@
 import { Decoder, Encoder, Packet, PacketType } from "socket.io-parser";
 import debugModule = require("debug");
+import url = require("url");
 import type { IncomingMessage } from "http";
 import type { Namespace, Server } from "./index";
 import type { Socket } from "./socket";
@@ -222,7 +223,12 @@ export class Client {
    */
   private ondecoded(packet: Packet): void {
     if (PacketType.CONNECT === packet.type) {
-      this.connect(packet.nsp, packet.data);
+      if (this.conn.protocol === 3) {
+        const parsed = url.parse(packet.nsp, true);
+        this.connect(parsed.pathname!, parsed.query);
+      } else {
+        this.connect(packet.nsp, packet.data);
+      }
     } else {
       const socket = this.nsps.get(packet.nsp);
       if (socket) {

test/socket.io.ts

@@ -2479,6 +2479,32 @@ describe("socket.io", () => {
       });
     });
 
+    it("should be able to connect to a namespace with a query", (done) => {
+      const srv = createServer();
+      const sio = new Server(srv, {
+        allowEIO3: true,
+      });
+
+      srv.listen(async () => {
+        const port = (srv.address() as AddressInfo).port;
+        const clientSocket = io_v2.connect(
+          `http://localhost:${port}/the-namespace`,
+          {
+            multiplex: false,
+          }
+        );
+        clientSocket.query = { test: "123" };
+
+        const [socket]: Array<any> = await Promise.all([
+          waitFor(sio.of("/the-namespace"), "connection"),
+          waitFor(clientSocket, "connect"),
+        ]);
+
+        expect(socket.handshake.auth).to.eql({ test: "123" });
+        success(sio, clientSocket, done);
+      });
+    });
+
     it("should not connect if `allowEIO3` is false (default)", (done) => {
       const srv = createServer();
       const sio = new Server(srv);