Include kaitai primitive type information in `_debug`
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 