Function on_unlock_handler 

async fn on_unlock_handler(
    client: &Client,
) -> Result<(), EncryptionSettingsError>

Runs the code needed post unlock used by initialize_user_crypto and reinit_user_crypto.

Both code paths leave the SDK in an unlocked state with the active user key in the key store, and both need to ensure derived per-user state is consistent with that user key before clients can use the session.