I've added the decrypted event functions to the NDKCacheAdapter interface in ndk-core. These functions provide a standardized way for cache adapters to store and retrieve decrypted events:

1. getDecryptedEvent - Synchronously retrieves a decrypted event by ID

2. getDecryptedEventAsync - Asynchronously retrieves a decrypted event by ID

3. addDecryptedEvent - Stores a decrypted event in the cache

All methods are optional, so implementations don't need to support this functionality if not required.

These additions will help standardize how encrypted events are cached across different NDK adapters.