feat(retry): add retry feature

[wantbook-book]

Issue resolved by this Pull Request:
Resolves #2465

Introduced a reusable retry-enabled HTTP helper (docling.utils.http_client) and refactored all existing remote requests calls to use it. This makes download helpers, HTML backend image fetches, and OpenAI-compatible image requests more resilient to transient errors and rate limiting without duplicating retry configuration.

Checklist:

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

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Related Documentation

Checked 5 published document(s) in 1 knowledge base(s). No updates required.

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Codecov Report

❌ Patch coverage is 51.51515% with 16 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
docling/utils/http_client.py	52.00%	12 Missing ⚠️
docling/utils/api_image_request.py	50.00%	2 Missing ⚠️
docling/backend/html_backend.py	50.00%	1 Missing ⚠️
docling/utils/utils.py	50.00%	1 Missing ⚠️

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[cau-git]

@wantbook-book Many thanks for the effort, this looks definitely useful. However, some tests are failing. Could you please review those?

To run locally:

uv run pytest tests/ -s -v # Note: some tests may fail related to OCR/webp if you don't have TESSDATA_PREFIX env set up. The tests failing in CI are not related to these.

[wantbook-book]

I ran uv run pytest tests/ -s -v locally, and a lot of TypeError: StringConstraints() takes no arguments errors appeared, for example:

==================================== ERRORS ====================================
________________ ERROR collecting tests/test_asr_mlx_whisper.py ________________
tests/test_asr_mlx_whisper.py:12: in <module>
    from docling.datamodel.asr_model_specs import (
docling/datamodel/asr_model_specs.py:9: in <module>
    from docling.datamodel.pipeline_options_asr_model import (
docling/datamodel/pipeline_options_asr_model.py:8: in <module>
    from docling.datamodel.pipeline_options_vlm_model import (
docling/datamodel/pipeline_options_vlm_model.py:4: in <module>
    from docling_core.types.doc.page import SegmentedPage
.venv/lib/python3.9/site-packages/docling_core/types/__init__.py:8: in <module>
    from docling_core.types.doc.document import DoclingDocument
.venv/lib/python3.9/site-packages/docling_core/types/doc/__init__.py:9: in <module>
    from .document import (
.venv/lib/python3.9/site-packages/docling_core/types/doc/document.py:39: in <module>
    from docling_core.search.package import VERSION_PATTERN
.venv/lib/python3.9/site-packages/docling_core/search/package.py:23: in <module>
    class Package(BaseModel, extra="forbid"):
.venv/lib/python3.9/site-packages/docling_core/search/package.py:30: in Package
    version: Annotated[str, StringConstraints(strict=True, pattern=VERSION_PATTERN)] = (
E   TypeError: StringConstraints() takes no arguments

Do you have any suggestions for how to fix this?