This PR introduces an option to utilize a custom serializer for serializing the store state before it is transmitted using broadcast-channel. This is essential because the Pinia store state is a proxy, and broadcast-channel only supports the transmission of POJOs or strings. By default, it uses JSON.stringify/JSON.parse for serialization.

Additionally, this update eliminates the need for individual state watches, opting instead for the built-instore.$subscribe feature provided by Pinia.

Closes #29 but might reintroduce #27.

Example usage:

import { PiniaSharedState } from 'pinia-shared-state'
import { parse, stringify } from 'zipson' // Choose whatever suits your project.

pinia.use(
  PiniaSharedState({
    serializer: {
      serialize: stringify,
      deserialize: parse,
    },
  }),
)