fix(14a): raw() returns whole firmware buffer instead of received bytes

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>

tests/test_hf_14a.py

@@ -25,6 +25,31 @@ def test_14a_scan():
     assert result["sak"] == 0x08
 
 
+def test_14a_raw_trims_to_received_length():
+    t = AsyncMock()
+    hf14a = HF14ACommands(t)
+    # firmware replies with its whole (padded) buffer; oldarg[0] = bytes actually received
+    version = bytes.fromhex("0004040201000f03") + b"\x80\x91"   # 8-byte version + 2-byte CRC
+    t.send_mix.return_value = PM3Response(cmd=Cmd.ACK, status=0, reason=0, ng=False,
+                                          data=version + b"\x00" * 30, oldarg=[10, 0, 0])
+    result = asyncio.get_event_loop().run_until_complete(hf14a.raw(b"\x60"))
+    assert result["received"] == 10
+    assert result["raw"] == version            # trimmed to the received length, not the padding
+    assert result["data"] == version.hex()
+
+
+def test_14a_raw_no_response_is_empty():
+    t = AsyncMock()
+    hf14a = HF14ACommands(t)
+    # tag didn't answer: received length 0, buffer full of zeros -> must come back empty
+    t.send_mix.return_value = PM3Response(cmd=Cmd.ACK, status=0, reason=0, ng=False,
+                                          data=b"\x00" * 40, oldarg=[0, 0, 0])
+    result = asyncio.get_event_loop().run_until_complete(hf14a.raw(b"\x30\x99"))
+    assert result["received"] == 0
+    assert result["raw"] == b""                # not 40 bytes of zeros
+    assert result["data"] is None
+
+
 def test_14a_sim_packs_ng_struct():
     t = AsyncMock()
     hf14a = HF14ACommands(t)