disentangle model from tuner and rename modules

src/llmtuner/train/rm/metric.py

@@ -0,0 +1,7 @@
+import numpy as np
+from typing import Dict, Sequence, Tuple, Union
+
+
+def compute_accuracy(eval_preds: Sequence[Union[np.ndarray, Tuple[np.ndarray]]]) -> Dict[str, float]:
+    preds, _ = eval_preds
+    return {"accuracy": (preds[0] > preds[1]).sum() / len(preds[0])}