fix: eval script bugs and add missing features

- evaluate_mmlu: fix double few-shot injection (build_prompt no longer
  adds few-shot, apply_chat handles it once)
- evaluate_humaneval: fix pass@k k-filtering to be per-problem instead
  of using first problem's n globally; reuse ProcessPoolExecutor across
  problems; fix closure UnboundLocalError in test_one; handle None in
  report when k > n
- evaluate_ifd: remove dead code (score_plain/score_messages); add
  multi-file/directory input support with --input_path/--output_dir;
  add summary.json aggregation and --max_samples; add --dtype flag
- evaluate_ppl: add --device and --dtype flags (was hardcoded to cuda)
- evaluate_ifeval: fix docstring path (scripts/tools -> scripts/eval)
- analyze_weights: add --output JSON export; fix dead code filter
  ("_norm" not in r was always True)

scripts/eval/evaluate_ifeval.py

@@ -5,7 +5,7 @@ Supports all IFEval constraint types except language detection.
 
 Usage::
 
-    python scripts/tools/evaluate_ifeval.py --param_path ./params \
+    python scripts/eval/evaluate_ifeval.py --param_path ./params \
         --data_path ifeval.jsonl --output results.json \
         --temperature 0.1 --max_tokens 512
 """