JsonFormatter and BufferedJsonFormatter move verbatim out of
WResp.cpp/WResp.h, which now include JsonFormatter.h. They don't need
the web server, so on their own they can be unit tested on the PC; the
native env builds the new file. AsyncJsonResp and JsonSockEvent stay
in WResp. No behaviour change.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
