Function get_device_source 

pub fn get_device_source(
    device: Option<&str>,
    config: &Config,
) -> (Option<String>, Option<&'static str>)

Get info about whether we’re using a fallback device. Returns (device_identifier, fallback_source) where fallback_source is:

• None if device was explicitly provided
• Some(“default”) if using default device
• Some(“last”) if using last connected device
• Some(“store”) if using known device from database