fix: keep the concrete type in the set-members fingerprint marker

The 6d370a4 determinism rewrite collapsed the set-value marker from
f'{type(value).__name__}:members' to a bare '\x00set:members', so a set value and a
frozenset value with the same members fingerprinted identically - a fix-introduced
collision that contradicts the same commit's collision-resistance claim. Restore the
concrete type in the marker (keeping the \x00 prefix so it stays uncollidable with a
user string key). Determinism across processes is unaffected.

Signed-off-by: disqualifier <dev@disqualifier.me>

src/envelope_crypto/envelope_crypto.py

@@ -681,7 +681,9 @@ def _fingerprint_normalize(value: Any) -> Any:
     if isinstance(value, (set, frozenset)):
         members = [_fingerprint_normalize(item) for item in value]
         members.sort(key=lambda item: json.dumps(item, sort_keys=True, default=_fingerprint_default))
-        return {"\x00set:members": members}
+        # keep the concrete type in the marker so a set value and a frozenset value with the
+        # same members stay distinct; the \x00 prefix keeps it uncollidable with a user str key
+        return {f"\x00{type(value).__name__}:members": members}
     if isinstance(value, (list, tuple)):
         return [_fingerprint_normalize(item) for item in value]
     return value