G1: NEW-B — wrap parsePacketPayload ADVERT branch in try/except

The ADVERT branch in MeshcorePacketParser.parsePacketPayload reads the
flags byte with `pk_buf.read(1)[0]`, which IndexErrors on a short
advert payload (the minimum advert is 32 + 4 + 64 + 1 = 101 bytes
before any optional fields). Pre-F06, the IndexError would escape as a
swallowed task exception. With F06's umbrella now in place it would
log and skip the dispatch, but the proposal §4.1 NEW-B asks for a
narrower local guard so a malformed advert doesn't poison the rest of
the parse path.

The optional `lat/lon/feat1/feat2` reads after the flags byte also
silently produce zeros on short reads (`int.from_bytes(b"", ...)`
returns 0), which would propagate bogus zero coordinates upstream.
Wrapping the whole branch limits the blast radius to a single
malformed advert.

Wrap the entire body of the ADVERT elif (from `pk_buf = io.BytesIO(...)`
through the final `log_data["adv_feat2"]` assignment) in
`try/except (IndexError, ValueError)` and log a debug message with the
exception type, message, and `pkt_payload` length on failure. This
matches the defensive pattern the proposal specifies.

Finding: NEW-B (S3)
File: src/meshcore/meshcore_parser.py

src/meshcore/meshcore_parser.py

@@ -171,6 +171,7 @@ class MeshcorePacketParser:
                 del self.channels_log[:25]
 
         elif not payload is None and payload_type == 0x04: # Advert
+            try:
                 pk_buf = io.BytesIO(pkt_payload)
                 adv_key = pk_buf.read(32).hex()
                 adv_timestamp = int.from_bytes(pk_buf.read(4), "little", signed=False)
@@ -205,5 +206,7 @@ class MeshcorePacketParser:
                     log_data["adv_feat1"] = adv_feat1
                 if not adv_feat2 is None:
                     log_data["adv_feat2"] = adv_feat2
+            except (IndexError, ValueError) as e:
+                logger.debug(f"parsePacketPayload: malformed ADVERT payload ({type(e).__name__}: {e}), len={len(pkt_payload)}")
 
         return log_data