pub trait UsageGainListenerProxyInterface: Send + Sync {
    type OnGainMuteChangedResponseFut: Future<Output = Result<(), Error>> + Send;
    // Required method
    fn on_gain_mute_changed(
        &self,
        muted: bool,
        gain_dbfs: f32,
    ) -> Self::OnGainMuteChangedResponseFut;
}