[Benchmark Backfill] Integrate CountBench into lmms-eval

[Luodian]

Summary

• Add a new countbench task backed by vikhyatk/CountBenchQA (test split) with the CountBenchQA reference prompt style.
• Implement task utilities for image/text conversion and source-aligned count normalization (number words -> numerals) with exact-match accuracy scoring.
• Update docs/current_tasks.md to include CountBench in the image task catalog.

Validation

• uv run python -m lmms_eval --tasks list (verified countbench is listed)
• uv run python -m lmms_eval --model dummy_video_reader --model_args response=2 --tasks countbench --limit 8 --batch_size 1
• uv run pre-commit run --files docs/current_tasks.md lmms_eval/tasks/countbench/countbench.yaml lmms_eval/tasks/countbench/utils.py

Notes

• YAML LSP reports unresolved !function tags for task YAMLs by default; this matches existing task files in the repo.

Smoke Validation (limit=8)

Status: PASS (LMM-291 / countbench)

Output Table

Metric	Value
acc	0.875

Sample Output

Sample 1 (doc_id: 0)

• Input: Look at the image carefully and count the objects. Answer with just a number, without any additional text. How many headsets are there in the image?
• Model Output: 10
• Reference: 10
• Scores: acc = 1.0
• Tokens: output=153, reasoning=151

Sample 2 (doc_id: 1)

• Input: Look at the image carefully and count the objects. Answer with just a number, without any additional text. How many light bulbs are there in the image?
• Model Output: 3
• Reference: 3
• Scores: acc = 1.0
• Tokens: output=57, reasoning=56

Test Params

uv run python -m lmms_eval --model openai_compatible --model_args "model_version=bytedance-seed/seed-1.6-flash" --tasks countbench --batch_size 1 --limit 8 --log_samples