feat: add TimeLens benchmark

[kcz358]

Summary

• Adds TimeLens temporal grounding tasks for ActivityNet, Charades, and QVHighlights.
• Uses kcz358/timelens with lmms-eval's existing dataset video zip extraction flow.
• Reports Charades-STA IOU@3, IOU@5, IOU@7, and mIOU directly in lmms-eval results.

Dataset Assets

• Uploaded 18 video zip archives to kcz358/timelens under videos/.
• Verified every archive is below 5GB and preserves relative paths such as charades/<video>.mp4.

Testing

• pre-commit run --files lmms_eval/tasks/timelens/timelens.yaml lmms_eval/tasks/timelens/_default_yaml_template lmms_eval/tasks/timelens/timelens_activitynet.yaml lmms_eval/tasks/timelens/timelens_charades.yaml lmms_eval/tasks/timelens/timelens_qvhighlights.yaml lmms_eval/tasks/timelens/utils.py lmms_eval/tasks/charades_sta/charades.yaml lmms_eval/tasks/charades_sta/utils.py
• python -m compileall -q lmms_eval/tasks/timelens lmms_eval/tasks/charades_sta
• scripts/run_timelens_qwen3vl4b.sh with LIMIT=4
• Focused Charades-STA parsing and direct metric aggregation smoke checks.