Trying to use '_debug' metadata in view
I'm using the Kaitai Python runtime in https://github.com/Mahlet-Inc/hobbits to make a Kaitai runner and viewer plugin. It works in a few cases, but a user pointed out a pretty simple case in which it fails to calculate offsets correctly: https://github.com/Mahlet-Inc/hobbits/issues/93

Here is the ksy:

```ksy
meta:
  file-extension: bla
  id: servermod
  endian: le
  imports:
    - /serialization/google_protobuf
seq:
  - id: records
    type: record
    repeat: eos
types:
  main_header:
    seq:
      - id: ip1
        type: u1
      - id: ip2
        type: u1
      - id: ip3
        type: u1
      - id: ip4
        type: u1
      - id: body_len
        type: u4le
  record:
    seq:
      - id: len_record
        type: main_header
        doc: Size of whole record, including all headers, footers and data
      - id: ctype
        type: u1
        doc: ctype
      - id: flow
        type: u1
        doc: flow
      - id: cid
        type: u4le
        doc: cid
      - id: did
        type: u4le
        doc: did
      - id: seq1
        type: u8le
        doc: seq1
      - id: command
        type: u2le
        doc: command
      - id: protobuf
        size: len_record.body_len - 24
        type: google_protobuf
```

Here is where I hit a roadblock:

Sometimes the "_debug" metadata from the parse has an absolute offset, for example with the `records[1].len_record` section:

```python
{ '_debug': defaultdict(<class 'dict'>,
                        { 'body_len': {'end': 46, 'start': 42},
                          'ip1': {'end': 39, 'start': 38},
                          'ip2': {'end': 40, 'start': 39},
                          'ip3': {'end': 41, 'start': 40},
                          'ip4': {'end': 42, 'start': 41}}),
  '_io': <kaitaistruct.KaitaiStream object at 0x7fff98348070>,
  '_parent': <servermod.Servermod.Record object at 0x7fff60bae8b0>,
  '_root': <servermod.Servermod object at 0x7fff98368df0>,
  'body_len': 34,
  'ip1': 47,
  'ip2': 254,
  'ip3': 184,
  'ip4': 155}
```

But for the `records[1].protobuff` section, everything resets to relative offsetting:

```python
{ '_debug': defaultdict(<class 'dict'>,
                        { 'pairs': { 'arr': [ {'end': 2, 'start': 0},
                                              {'end': 10, 'start': 2}],
                                     'end': 10,
                                     'start': 0}}),
  '_io': <kaitaistruct.KaitaiStream object at 0x7fff60bae730>,
  '_parent': None,
  '_root': <google_protobuf.GoogleProtobuf object at 0x7fff60bae6d0>,
  'pairs': [ <google_protobuf.GoogleProtobuf.Pair object at 0x7fff60bae670>,
             <google_protobuf.GoogleProtobuf.Pair object at 0x7fff60bae580>]}
```

There might be a pattern to when it is relative (in which case I could get the absolute offset from the parent chunk), but I don't notice any such pattern.

I don't know much about kaitai, so it's likely that I'm missing something simple here, but I thought I'd ask for help since I can't find any documentation for parsing the python "_debug" section.