fix(ocr): warn when LLM extraction fails

[Chisa Kotegawa (DEOWL-kan)]

Summary

• emit a Python warning when LLM Vision OCR catches a client failure, so converter callers no longer hide it
• include only the exception type in the warning while preserving the original message in OCRResult.error
• add a regression test for warning visibility, error preservation, sensitive-message exclusion, and stream rewind

Fixes #2313.

Testing

• python -m pytest -q packages/markitdown-ocr/tests — 42 passed
• git diff --check

Not run locally: pre-commit (not installed in the test environment).

[Chisa Kotegawa (DEOWL-kan)]

@microsoft-github-policy-service agree