Tidy checkpoint step parsing

omnivae_generation/trainer/eval/guided_diffusion.py

@@ -77,7 +77,4 @@ def extract_checkpoint_step(checkpoint_dir: str | Path) -> int:
     """Best-effort training step for a checkpoint directory name."""
     name = Path(checkpoint_dir).expanduser().resolve().name
     match = _CKPT_STEP_RE.search(name)
-    if match:
-        return int(match.group(1))
-    digits = re.findall(r"\d+", name)
-    return int(digits[-1]) if digits else 0
+    return int(match.group(1)) if match else 0