// Serial support has a POSIX termios backend (`serial_port.rs`) and a Win32
// DCB backend (`serial_port_win32.rs`), mirroring C asyn's split between
// `drvAsynSerialPort.c` and `drvAsynSerialPortWin32.c`. Both expose the same
// `serial_port` module path so callers (iocsh, the port registry) need no
// per-platform gating — the build selects one, like C's `OS_CLASS` Makefile
// switch.