[feature] provider adapter for async storage

[rclai]

What problem does this new feature solve?

It would be nice to have the ability to pass an adapter to use the async storage library of choice like mmkv, similar to the clipboard property you guys have.

Describe the solution you'd like

import { MMKV } from 'react-native-mmkv';

const mmkv = new MMKV();

export interface AsyncStorageAdapter {
  getItem: (key: string) => Promise<string | null>;
  setItem: (key: string, value: string) => Promise<void>;
  removeItem: (key: string) => Promise<void>;
  // Optional: Additional methods like clear() or multiGet() if needed by AppKit
}

// Custom storage adapter implementation
const customStorageAdapter: AsyncStorageAdapter = {
  getItem: async (key: string) => {
    return mmkv.getString(key) ?? null;
  },
  setItem: async (key: string, value: string) => {
    mmkv.set(key, value);
  },
  removeItem: async (key: string) => {
    mmkv.delete(key);
  },
};

createAppKit({
  storageAdapter: customStorageAdapter, // Pass the custom storage adapter
  // ... other params
});

[itsnyx]

this is a duplicate issue see #352