chore: use mmkv as storage in wallet sample

[ignaciosantise]

Summary

• added react-native-mmkv for storage

[Copilot]

Pull Request Overview

This PR replaces AsyncStorage with react-native-mmkv for storage operations in the React Native wallet application. MMKV provides better performance and synchronous operations compared to AsyncStorage's asynchronous API.

Key changes:

• Added react-native-mmkv dependency and created a storage utility wrapper
• Replaced all AsyncStorage imports and usage with the new storage utility
• Updated iOS project configuration and removed unnecessary Xcode project entries

Reviewed Changes

Copilot reviewed 9 out of 11 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/utils/storage.ts	New storage utility wrapper providing async API over MMKV
src/utils/WalletKitUtil.ts	Updated to use new storage utility instead of AsyncStorage
src/utils/SuiWalletUtil.ts	Replaced AsyncStorage with storage utility for mnemonic operations
src/utils/EIP155WalletUtil.ts	Updated wallet initialization to use new storage utility
src/store/SettingsStore.ts	Migrated settings storage from AsyncStorage to new utility
src/screens/Settings/index.tsx	Updated settings screen to use new storage utility
package.json	Added react-native-mmkv dependency
ios/RNWeb3Wallet.xcodeproj/project.pbxproj	Cleaned up Xcode project configuration
ios/.xcode.env	Updated Xcode environment configuration

---

_{Tip: Customize your code reviews with copilot-instructions.md. Create the file or learn how to get started.}