iOSNotification generates duplicate identifiers when multiple notifications are created concurrently

Steps to reproduce:

1. Create or open any project
2. Confirm that Mobile Notifications is installed
3. Add attached C559IdentifierCollisionStress.cs to the Assets/Editor folder
4. Wait for script compilation to finish
5. Open Window > General > Console
6. Select Tools > Bug Repros > C559 Identifier Collision Stress
7. Wait for the test to create 2,000,000 iOSNotification objects concurrently
8. Observe the Console output:

Actual result: Many iOSNotification instances have duplicate automatically generated identifiers
Expected result: All 2,000,000 iOSNotification instances have unique automatically generated identifiers, and the Console reports Duplicates: 0

Reproducible with: 2.3.2 (6000.0.0f1), 2.5.0 (6000.0.85f1, 6000.3.27f1, 6000.6.7f1, 6000.7.0b6, 7000.0.0a10)

Reproducible on: MacOS 27.0 (M1 Max), Windows 10 (Reporter)
Not reproducible on: No other environments tested