fix(sniffer): mark JA3/JA3S MD5 hashing as non-security

JA3/JA3S fingerprints are defined by their specs as MD5 digests of
the ClientHello/ServerHello feature tuples — they are identifiers,
not security primitives. Pass usedforsecurity=False at the two call
sites so bandit stops flagging them as B324 High when scanning
outside the templates/ exclude.

decnet/templates/sniffer/server.py

@@ -639,7 +639,8 @@ def _ja3(ch: dict[str, Any]) -> tuple[str, str]:
         "-".join(str(p) for p in ch["ec_point_formats"]),
     ]
     ja3_str = ",".join(parts)
-    return ja3_str, hashlib.md5(ja3_str.encode()).hexdigest()
+    # JA3 fingerprint spec uses MD5; not security-relevant.
+    return ja3_str, hashlib.md5(ja3_str.encode(), usedforsecurity=False).hexdigest()
 
 
 def _ja3s(sh: dict[str, Any]) -> tuple[str, str]:
@@ -650,7 +651,8 @@ def _ja3s(sh: dict[str, Any]) -> tuple[str, str]:
         "-".join(str(e) for e in sh["extensions"]),
     ]
     ja3s_str = ",".join(parts)
-    return ja3s_str, hashlib.md5(ja3s_str.encode()).hexdigest()
+    # JA3S fingerprint spec uses MD5; not security-relevant.
+    return ja3s_str, hashlib.md5(ja3s_str.encode(), usedforsecurity=False).hexdigest()
 
 
 # ─── JA4 / JA4S computation ──────────────────────────────────────────────────