Cannot subclass BaseKeyProvider to use RTCKeyDerivationAlgorithmHKDF

BaseKeyProvider is public **final** class → cannot be subclassed. rtcKeyProvider is let with no access modifier → module-internal, unreadable and unassignable from app code, and its type LKRTCFrameCryptorKeyProvider lives behind internal import LiveKitWebRTC → also unreachable. Android's Kotlin SDK ships KeyProvider as an interface with val rtcKeyProvider as a contract member. iOS's wrapper is a final concrete class that owns its rtcKeyProvider privately, so the Android pattern has no direct iOS analog. Swift version affected: 2.14.0 Android version: https://github.com/livekit/client-sdk-android/releases/tag/v2.24.0