hf.iso14a.raw() returned the entire receive buffer the firmware replies
with (sizeof(buf)), so a tag that didn't answer came back as a run of
zeros (~40 bytes) rather than empty. The firmware puts the real received
length in oldarg[0]; trim resp.data to it. No response -> empty (raw=b"",
data=None); adds a `received` count. 2 regression tests.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
7b5af3f9d2