fix: add default_encoder fallback to msgpack.packb in write_frame

numpy dtype objects are not MessagePack-serializable and caused
TypeError when calling getAttr('dtype'). The default_encoder fallback
converts non-serializable objects to str() to prevent crashes.

Author: howtis

python-embed-runtime/src/main/resources/io/github/howtis/pythonembed/bridge.py

@@ -444,7 +444,7 @@ def read_frame(stream):
 
 def write_frame(stream, obj):
     """Write a dict as a length-prefixed MessagePack frame to a binary stream."""
-    data = msgpack.packb(obj)
+    data = msgpack.packb(obj, default=default_encoder)
     length = len(data)
     stream.write(struct.pack('>I', length))
     stream.write(data)