fix: remove unnecessary f-string prefixes and unused import (#2352)

- Remove f-string prefix on 7 strings with no placeholders (F541)
  in analyze.py, aggregate_benchmark.py, run_loop.py, generate_review.py
- Remove unused `os` import in quick_validate.py (F401)

Found by ruff via HUMMBL Arbiter (https://hummbl.io/audit).

skills/public/skill-creator/scripts/run_loop.py

@@ -188,7 +188,7 @@ def run_loop(
 
         # Improve the description based on train results
         if verbose:
-            print(f"\nImproving description...", file=sys.stderr)
+            print("\nImproving description...", file=sys.stderr)
 
         t0 = time.time()
         # Strip test scores from history so improvement model can't see them