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>

pm3py/core/hf_iso14a.py

@@ -63,10 +63,16 @@ class HF14ACommands:
             payload=data,
             timeout=5.0,
         )
+        # The firmware replies with its whole receive buffer; oldarg[0] is the number of bytes
+        # actually received (0 = the tag didn't answer). Trim to it so a no-response is empty,
+        # not a buffer of zeros.
+        received = resp.oldarg[0] if resp.oldarg else 0
+        payload = resp.data[:received] if resp.data else b""
         return {
             "status": resp.status,
-            "data": resp.data.hex() if resp.data else None,
-            "raw": resp.data,
+            "received": received,
+            "data": payload.hex() if payload else None,
+            "raw": payload,
         }
 
     async def sniff(self, param: int = 0) -> dict: