fix(typescript): overload batch for either array or spread args

[grddavies]

The typescript types for Database.batch allows spreading an array that includes an array of operations, despite the fact that this causes a runtime error:

This snippet shows how this can result in runtime errors:

import { Database, Model, appSchema, tableSchema } from '@nozbe/watermelondb'
import SQLiteAdapter from '@nozbe/watermelondb/adapters/sqlite'
import { text } from '@nozbe/watermelondb/decorators'

type Operation = Model | Model[]

export const schema = appSchema({
  version: 1,
  tables: [
    tableSchema({
      name: 'foo',
      columns: [{ name: 'bar', type: 'string' }],
    }),
  ],
})

class FooModel extends Model {
  static table = 'foo'
  @text('bar') bar!: string
}

const database = new Database({
  adapter: new SQLiteAdapter({ dbName: ':memory:', schema }),
  modelClasses: [FooModel],
})

export class Transaction {
  private readonly ops: Operation[] = []

  register(...operations: Operation[]): void {
    this.ops.push(...operations)
  }

  async commit(database: Database): Promise<void> {
    const ops = this.ops.splice(0)
    await database.write(() => database.batch(...ops))
  }
}

const tx = new Transaction()

let i = 0
const createModel = () =>
  database
    .get<FooModel>('foo')
    .prepareCreate((record) => (record.bar = `${i++}`))

async function main() {
  // works
  tx.register(createModel())
  await tx.commit(database)
  console.log('ok')

  // works
  tx.register([createModel(), createModel()])
  await tx.commit(database)
  console.log('ok')

  // TypeError: Cannot read properties of undefined (reading '_status')
  tx.register(createModel(), [createModel(), createModel()])
  await tx.commit(database)
  console.log('ok?')
}

main()

After updating the type definitions we get a compiler error in Transaction.commit:

Type 'Model[]' is not assignable to type 'false | void | Model | null'. ts (2345)

May be related to #1952