feat(asr): expose beam_size and condition_on_previous_text (native)

[BBC-Esq]

Issue resolved by this Pull Request:
Resolves #3703

What

The native (openai-whisper) ASR backend forwarded only verbose and word_timestamps to transcribe() and exposed no decoding parameters on InlineAsrNativeWhisperOptions. With whisper's default greedy decoding (beam_size=None), long-form audio can spiral into runaway repetition and effectively hang, with no workaround available through the docling API. Root-cause isolation and benchmarks are in #3703.

This exposes two of whisper's decoding parameters on InlineAsrNativeWhisperOptions and forwards them in the native transcribe() call:

• beam_size: Optional[int] = None
• condition_on_previous_text: bool = True

Both default to whisper's own defaults, so existing behaviour is unchanged. Setting beam_size=5 (beam search) or condition_on_previous_text=False reliably avoids the repetition hang on long-form audio.

Modified files

• docling/datamodel/pipeline_options_asr_model.py — added beam_size and condition_on_previous_text to InlineAsrNativeWhisperOptions.
• docling/pipeline/asr_pipeline.py — read both in _NativeWhisperModel and forward them in transcribe().
• tests/test_asr_pipeline.py — added test_native_whisper_forwards_decode_params.

Notes

• Conservative defaults on purpose. I kept the defaults equal to whisper's rather than switching the default to beam search, to avoid changing existing output. Happy to default beam_size to a non-greedy value (e.g. 5) if you'd prefer the hang fixed out-of-the-box.
• temperature and language were intentionally left out: forwarding temperature=0.0 would change transcription output, and the option's language="en" default would regress non-English audio. Glad to add them in a follow-up if wanted.

Checklist:

• Documentation has been updated, if necessary. (The new options are self-documenting via their Field(description=...).)
• Examples have been added, if necessary. (Not necessary — config-only change.)
• Tests have been added, if necessary.

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