Include kaitai primitive type information in `_debug`

[hello-adam]

When a spec with a primitive type (e.g. u*, f*, s*be, etc.) is parsed, that type data is not plainly available in the KaitaiStruct or its _debug data (at least not in Python). It would be nice to not need to infer the primitive type from a combination of the Python type, byte range, value, and actual data. One example case: Mahlet-Inc/hobbits#110

[KOLANICH]

#896