fix: add type declaration in package.json

[thorseraq]

Fix potential errors when import using import {WebsocketProvider} from 'y-websocket'; in typescript project

TS7016: Could not find a declaration file for module 'y-websocket'. '/Users/xiaotian/WebstormProjects/affine-demo-thorseraq/node_modules/.pnpm/[email protected][email protected]/node_modules/y-websocket/src/y-websocket.js' implicitly has an 'any' type.   There are types at '/Users/xiaotian/WebstormProjects/affine-demo-thorseraq/node_modules/y-websocket/dist/src/y-websocket.d.ts', but this result could not be resolved when respecting package.json "exports". The 'y-websocket' library may need to update its package.json or typings.