`ParsingSettings.disable_doc_valid_check` superceded by contents length

Due to https://github.com/Future-House/paper-qa/blob/v5.21.0/paperqa/docs.py#L409-L422, when building a local index, the `ParsingSettings.disable_doc_valid_check` is bypassed on:

- Empty code files such as `py.typed`
- Nearly-empty files such as `.python-version`

Ideally we have a way to include these files in a built index.