Ping sends DEVICE_PING frame and waits for DEVICE_INFO response.
Read sends PARAM_READ frame and waits for matching PARAM_ENTRY.
Both use cel_crsf_stream_feed() with a clock-based timeout loop.
Implement cel_serial_find_elrs_port() which enumerates serial ports
and matches descriptions against ELRS-related keywords (CP210, CH340,
FTDI, etc.). Implement cel_serial_open_probe() to try multiple baud
rates in order.
Add cel_serial_platform_get_description() for Windows (SetupAPI)
and POSIX (sysfs fallback). Wire setupapi into the Windows build.
Update serial tests with CMock expectations for the new functions.
portersky