//! Non-blocking byte-stream transport trait.
//!
//! Any byte-stream I/O source/sink implements [`Transport`]. For nRF52840-DK,
//! see `rtt_transport::RttTransport` in the example crate.
/// Non-blocking byte-stream transport.
///
/// Both methods are non-blocking and return the number of bytes transferred.
/// Returning `0` means no bytes were available (read) or the sink was full
/// (write). Callers must poll in a loop rather than block.