feat: new artifacts path for old and new models and CLI utility

[dolfim-ibm]

Fix the location of local models for CodeFormula and PictureClassifier.

When the parameter artifacts_path is provided, the folder must have the following structure:

./mymodels/
├── CodeFormula/               # optional, only when activated
├── DocumentFigureClassifier/  # optional, only when activated
└── docling-models/
    └── model_artifacts/
        ├── layout/
        └── tableformer/

For backwards compatibility, we still support setting artifacts_path=mymodels/docling-models, but a deprecation warning is raised.

New CLI utility to download all model artifacts:

$ docling-models download
Downloading layout model...
Fetching 11 files: 100%|████████████████████████████████████████████████████████████████████████████████████████████████| 11/11 [00:00<00:00, 5200.92it/s]
Downloading tableformer model...
Fetching 11 files: 100%|████████████████████████████████████████████████████████████████████████████████████████████████| 11/11 [00:00<00:00, 3944.37it/s]
Downloading picture classifier model...
Fetching 4 files: 100%|███████████████████████████████████████████████████████████████████████████████████████████████████| 4/4 [00:00<00:00, 1050.74it/s]
Downloading code formula model...
Fetching 12 files: 100%|████████████████████████████████████████████████████████████████████████████████████████████████| 12/12 [00:00<00:00, 1990.49it/s]
Downloading easyocr models...
100%|████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 73.7M/73.7M [00:04<00:00, 16.9MB/s]
100%|████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 13.4M/13.4M [00:00<00:00, 14.3MB/s]
100%|████████████████████████████████████████████████████████████████████████████████████████████████████████████████| 13.6M/13.6M [00:00<00:00, 15.5MB/s]
All models downloaded in the directory /Users/dol/.cache/docling/models.

 Docling can now be configured for running offline using the local artifacts.

 Using the CLI: docling --artifacts-path={output_dir} FILE 
 Using Python: see the documentation at <https://ds4sd.github.io/docling/usage>.

Issue resolved by this Pull Request:
Resolves #870

Checklist:

• Documentation has been updated, if necessary.
• Examples have been added, if necessary.
• Tests have been added, if necessary.

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[cau-git]

@dolfim-ibm Do we want a separate CLI utility, or have it integrate into docling CLI such as docling models download

[dolfim-ibm]

@dolfim-ibm Do we want a separate CLI utility, or have it integrate into docling CLI such as docling models download

Adding a new command in docling will require to force users doing docling convert FILE, which I find more annoying than the separate CLI.

Alternatively, we could package all utilities into a single CLI, like doclig-tools models download or doclig-utils models download, or others