Related: socketio/socket.io#4719

So that debug logs can be printed with vite:

```js
import { defineConfig } from 'vite'
import react from '@vitejs/plugin-react'

export default defineConfig({
  plugins: [react()],
  server: {
    port: 4000
  },
  resolve: {
    conditions: ["development"]
  }
})
```

Reference: https://v2.vitejs.dev/config/#resolve-conditions

Related: socketio/socket.io-client@781d753

This reverts the previous commit ([1]), and expose the ESM build that
includes the debug package on a subpath:

```js
import { Socket } from "engine.io-client/debug";
```

Reference: https://nodejs.org/api/packages.html#subpath-exports

Related: https://github.com/socketio/socket.io-client/issues/1586

[1]: fe4d93a

Silently closing the connection when receiving a "beforeunload" event
is problematic, because it is emitted:

- when downloading a file from another host

Related: socketio/socket.io#4436

- when the user already has a listener for the "beforeunload" event
(i.e. "are you sure you want to leave this page?")

Related:

- #661
- #658
- socketio/socket.io#4065

That's why the `closeOnBeforeunload` option will now default to false.

Diff: 6.5.0...6.5.1