feature: support ImageRefMode.NONE

[geoHeil]

Currently ImageRefMode only reasons about a single representation of the document https://github.com/docling-project/docling-core/blob/main/docling_core/types/doc/base.py#L9-L14 and can embed, or refernece the image - or set a placeholder.

In case of a data pipelien where the same document should be stored in different representations (raw json, plus HTML for example)

document.save_as_json(
    Path(f"{mypath}.json"), image_mode=ImageRefMode.REFERENCED
)
document.save_as_html(
    Path(f"{mypath}.html"), image_mode=ImageRefMode.REFERENCED
)
document.save_as_markdown(
    Path(f"{mypath}.md"), image_mode=ImageRefMode.REFERENCED
)

by setting ImageRefMode.REFERENCED 3x the IO is incurred - instead setting the 1st one to REFERENCED and others to NONE would save resources/ be faster:

document.save_as_json(
    Path(f"{mypath}.json"), image_mode=ImageRefMode.REFERENCED
)
document.save_as_html(
    Path(f"{mypath}.html"), image_mode=ImageRefMode.NONE
)
document.save_as_markdown(
    Path(f"{mypath}.md"), image_mode=ImageRefMode.NONE
)

Would this be a sensible addition?

Or possibly modifying _with_pictures_refs to only generate the output if it does not already exist might be an alternative solution

[dolfim-ibm]

I think in this case one could "dump the images" and turn the document to a reference-flavour, then simply use REFERENCED as mode.

But if I'm not mistaken the functions for doing this "dump" are only internal/private.

[geoHeil]

But currently, REFERENCED would re-compute the images and not chache the IO in case the file already exists.