fix(docling): stringify binary_hash in document metadata

[vedjaw]

Related Issues

• fixes DoclingConverter: binary_hash metadata can exceed signed 64-bit integer range #3604

Proposed Changes:

DoclingConverter / MetaExtractor previously copied Docling's origin.binary_hash into Haystack document metadata as an integer. That value is an unsigned 64-bit hash, so values greater than 2**63 - 1 break document stores that map numeric metadata to signed 64-bit types (e.g. OpenSearch long).

Following the maintainer suggestion on #3604, binary_hash is now always stored as a string. The conversion is applied recursively in both extract_dl_doc_meta and extract_chunk_meta, so nested occurrences from chunk JSON are covered as well.

This is a breaking metadata-type change for callers that assumed binary_hash was an int.

How did you test it?

• Added unit tests for oversized binary_hash in document and chunk metadata paths
• Added a recursive helper test covering nested dicts/lists and None
• Ran: pytest tests/test_converter.py::TestMetaExtractor tests/test_converter.py::test_stringify_binary_hash_recursively (8 passed)
• ruff check on the touched files

Notes for the reviewer

• Approach matches @julian-risch's guidance on DoclingConverter: binary_hash metadata can exceed signed 64-bit integer range #3604 (binary_hash: str + major release of the integration).
• Version bump / release tagging left to maintainers (hatch-vcs tag-driven). CHANGELOG Unreleased entry marks the change as breaking.

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added unit tests and updated the docstrings
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test:.

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[anakin87]

CLA never signed, superseded by #3699