[Fix] fix MathCanvas-Bench md5 & summarize_mathcanvas_results

[shiwk24]

Summary

Fixes two issues affecting MathCanvas-Bench usage and reporting.

Changes

• Dataset MD5: Update MathCanvas-Bench checksum in image_vqa.py so the local TSV matches the current file and avoids unnecessary re-download / mismatch warnings.
• Summary stats (summarize_mathcanvas_results in mathcanvas.py): Align by_question_image_count and by_knowledge keys with the dataset so per-category and image-presence metrics count correctly (previously keys did not match).

Notes

No change to the judging logic; reporting / aggregation only, plus the hash update.

[clintonsteiner]

@dependabot rebase