Ryan Malloy
a2dcd6d58d
Harden OBD-II K-line handler (code review findings)
Fix UART pin detach: pinMatrixOutDetach() instead of no-op
uart_set_pin(ALL_NO_CHANGE). Fix timeout underflow in
readResponse() with remainingMs() helper. Add checksum
validation on received frames. Echo verification in clearEcho()
detects bus contention. Flush RX buffers after init sequences.
Structural ISO 14230 frame parsing replaces byte-scanning.
TesterPresent keepalive prevents P3 session timeout. Scanner
re-initializes after consecutive failures.