[MOB-11639] Make IterableKeychain Async to prevent ANRs

[sumeruchat]

MOB-11639: Fix IterableKeychain ANR Issues

Problem

was blocking the main thread with crypto operations, causing ANRs for customer PCLN.

Solution

• Implemented async cache pattern with immediate read access
• All methods now return instantly from cache
• All methods update cache immediately, save to storage in background
• Maintains full backward compatibility and thread safety

Changes

• Refactored to use for non-blocking cache
• Added comprehensive test suite (16 tests, all passing)
• Preserved all existing APIs and encryption behavior

Manual Testing Scenarios

1. Basic Functionality

• Initialize app with
• Call and immediately call
• ✅ Expected: Email returns instantly, no UI blocking

2. Rapid Successive Calls

• Make 10 rapid calls to , ,
• ✅ Expected: All calls return instantly (<1ms each), no ANRs

3. App Startup Performance

• Cold start the app and measure time to first UI interaction
• ✅ Expected: No delays from keychain operations, smooth startup

4. Background/Foreground Transitions

• Save user data, background app, foreground app, retrieve data
• ✅ Expected: Data persists correctly, no blocking on retrieval

5. Encryption Failure Recovery

• Simulate encryption failure (requires debug build)
• ✅ Expected: App continues functioning, falls back to plaintext

---

Status: ✅ Ready for Review
Tests: 16/16 passing
Backward Compatibility: Fully maintained