The real Arduino.h includes stdlib.h, so ConfigSerializer.cpp reaches atoi,
atol and atof through it and compiles on device. The mock supplied only
cstdint, cmath and Stream.h, leaving those undeclared — and since the native
env compiles ConfigSerializer.cpp into every suite via build_src_filter, all
21 suites errored rather than just its own.
Fixing the mock keeps src/ identical to upstream and covers any other source
relying on the same transitive include.
pio test -e native: 297 test cases, 297 succeeded.
Switch ESP32-S3 KISS modem environments to HWCDC and move outbound KISS writes to a non-blocking queued frame path so loop() and TX completion keep progressing when the host reads slowly. Add native backpressure regression tests and correct the native_kiss_modem test filter so this suite runs directly with pio test.