Function apply_debugger_mode 

pub fn apply_debugger_mode(
    debugger_mode: bool,
    driver: impl Spawn + Driver,
    name: &str,
    io: Box<dyn SerialIo>,
) -> Box<dyn SerialIo>

Wraps io in a DebuggerRelay (spawning a pump task on driver) when debugger_mode is set, otherwise returns io unchanged.

Shared by the serial device resolvers so the wrapping logic lives in one place.