Fix deprecated AppState.removeEventListener for React Native compatibility

[theAmit10]

Problem

This PR fixes a crash that occurs on iOS with newer React Native versions due to the use of deprecated AppState.removeEventListener.

Changes

• ✅ Store AppState subscription in component instance
• ✅ Use subscription.remove() instead of deprecated removeEventListener
• ✅ Maintains backward compatibility
• ✅ Fixes iOS crashes while preserving Android functionality

Code Changes

• Added this.appStateSubscription = null in constructor
• Changed AppState.addEventListener to store returned subscription
• Updated cleanup to use subscription.remove()

Testing

• ✅ Tested on iOS - no more crashes
• ✅ Tested on Android - works as before
• ✅ Backward compatible with older RN versions

Breaking Changes

None - this is a bug fix that maintains the same API.

Fixes #[133]