feat: expose ESM build with debug (#1585)

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#4731
- socketio/socket.io#4635
- https://github.com/socketio/socket.io-client/issues/1516

package.json

@@ -25,6 +25,7 @@
       "types": "./build/esm/index.d.ts",
       "import": {
         "node": "./build/esm-debug/index.js",
+        "development": "./build/esm-debug/index.js",
         "default": "./build/esm/index.js"
       },
       "require": "./build/cjs/index.js"