feat: support runtime progress bar overrides

[RAMZI0TO99]

Related Issues

• Fixes ENV variable to disable progress bar is not working #8782.
• Follows the invitation for a smaller replacement in #10389.

Proposed Changes:

Setting HAYSTACK_PROGRESS_BARS=0 now disables progress bars in the current core components, including their asynchronous execution paths. The override is read during execution, so changing the variable between runs takes effect on existing component instances without changing their stored or serialized progress_bar setting.

A private helper resolves case-insensitive, whitespace-trimmed values: 1, true, yes, and on enable progress bars; 0, false, no, and off disable them. Missing, empty, or unrecognized values preserve the component setting.

The helper is used by OpenAIDocumentEmbedder (also inherited by AzureOpenAIDocumentEmbedder), MarkdownToDocument, and LLMEvaluator (also used by FaithfulnessEvaluator and ContextRelevanceEvaluator). The FAQ, parameter docstrings, and release note describe the behavior.

How did you test it?

• 145 focused unit tests passed across the progress helper and the affected components, including inherited evaluator paths. New regressions cover runtime changes, both constructor defaults, synchronous/asynchronous behavior, and serialization. Embedding APIs are mocked.
• hatch run test:types passed: no issues in 553 source files.
• hatch run docs passed: all 28 API-reference configurations generated. On Windows, this required PYTHONUTF8=1 to match Linux CI's text encoding.
• The workflow-equivalent docusaurus-mdx-checker@3.0.0 passed on Node 22: all 28 generated API-reference pages and both edited FAQ pages compiled without errors.
• Full unit suite: 6,666 passed, 47 skipped, 338 deselected, and one failure. The failing CSV MIME-type test expects text/csv, while Windows returns application/vnd.ms-excel. It reproduces on clean upstream commit 87dba65; neither the test nor ByteStream is changed here.
• Ruff, syntax, YAML, whitespace, release-note formatting, and other applicable pre-commit hooks passed. Codespell passed using a local configuration that ignores caf, which appears in unchanged encoded-byte fixtures in the Markdown test module. The repository hook configuration is unchanged.

Tests were run through Hatch on Windows with Python 3.13.5. The test commands used --no-cov because coverage collection crashed during shutdown in this environment. The same test assertions still ran.

Notes for the reviewer

The implementation deliberately resolves the override at execution time and keeps the helper private. It covers the progress loops present in core; it does not modify components that have moved to integrations. The original constructor values remain the serialization source.

This PR was fully generated with an AI assistant. The implementation and regression coverage were reviewed using AI assistants, and the checks listed above were run. The contributor must personally review and understand the changes and accept the CLA; those personal requirements are not represented as completed here.

The PR remains a draft pending these requirements. Haystack's first-time-contributor CLA workflow returns unsigned PRs to draft. The upstream test, API-reference, release-note, and CodeQL workflows currently require maintainer approval to run, and the Vercel documentation preview requires team authorization. Maintainer edits are enabled.

Checklist

• Read the contributor guidelines and code of conduct.
• Updated the related issue with the implementation scope and validation results.
• Added unit tests and updated the docstrings and documentation.
• Used a conventional commit title.
• Added a release note.
• Ran applicable pre-commit checks, with the existing codespell fixture exception described above.
• Enabled maintainer edits on the contribution branch.
• Contributor personally reviews and understands the AI-generated changes.
• Contributor accepts the CLA at https://cla-assistant.io/deepset-ai/haystack?pullRequest=13093.

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