fix: separate client build

[EastSun5566]

Create a separate client build to prevent server code from being imported into the browser:

dist/
├── client
│   ├── index.cjs
│   ├── index.d.cts
│   ├── index.d.ts
│   └── index.js
├── index.cjs
├── index.d.cts
├── index.d.ts
└── index.js

2 directories, 8 files

---

Usage can be like that:

Server-side:

import { createYSocketIOServer, createWorker } from '@hackmd/y-socketio-redis'

Client-side:

import { SocketIOProvider } from '@hackmd/y-socketio-redis/client'