Wrong prefix for logs in KTOTrainer

[bartoszzuk]

The implementation of log method in KTOTrainer uses wrong prefix eval/ instead of eval_ (similar with train metrics).
This results in names of metrics not being properly processed by logging callbacks (I tested on WandbCallback). The problem is specifically with function rewrite_logs, which expects correct prefixes. This results in metric names in wandb like train/train/rewards/margins or train/eval/rewards/margins (see picture below). If you would like I can submit a pull request for this issue since the fix should be pretty trivial?

def rewrite_logs(d):
    new_d = {}
    eval_prefix = "eval_"
    eval_prefix_len = len(eval_prefix)
    test_prefix = "test_"
    test_prefix_len = len(test_prefix)
    for k, v in d.items():
        if k.startswith(eval_prefix):
            new_d["eval/" + k[eval_prefix_len:]] = v
        elif k.startswith(test_prefix):
            new_d["test/" + k[test_prefix_len:]] = v
        else:
            new_d["train/" + k] = v
    return new_d

[kawine]

thank for catching this @bartoszzuk ! please feel free to open a PR