Feature/persist watermelondb

[kvbalib]

This PR adds a first-class WatermelonDB LocalStorage persist plugin to @legendapp/state/sync. It enables fast, reliable persistence for React Native / Expo apps that use @nozbe/watermelondb, with synchronous reads.

•	Zero new runtime dependencies
•	No breaking changes

Changes

•	src/persist-plugins/watermelondb.ts (new)

Usage

import { observable } from '@legendapp/state'
import { syncObservable } from '@legendapp/state/sync'
import { observablePersistWatermelonDB } from '@legendapp/state/persist-plugins/watermelondb'
import { database } from '@/lib/db' // Watermelon Database

const settings$ = observable(true)

syncObservable(settings$, {
  persist: {
    name: 'settings',
    plugin: observablePersistWatermelonDB(database.localStorage),
  },
})