fix: Guard against crashes stemming from pdfium in threaded environments

[cau-git]

Checklist:

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

[mergify]

Merge Protections

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🟢 Enforce conventional commit

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Make sure that we follow https://www.conventionalcommits.org/en/v1.0.0/

• title ~= ^(fix|feat|docs|style|refactor|perf|test|build|ci|chore|revert)(?:\(.+\))?(!)?:

[github-actions]

✅ DCO Check Passed

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[codecov]

Codecov Report

❌ Patch coverage is 88.42105% with 22 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
docling/pipeline/standard_pdf_pipeline.py	71.21%	19 Missing ⚠️
docling/backend/managed_pdfium_backend.py	95.58%	3 Missing ⚠️

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[cau-git]

Closing in favour of #3180