Fix single gpu stat logging

[thejaminator]

Seems like we were forgetting to log the stats if the user selected to use a gpu.

So the csv output would be empty with only the columns e.g.

layer,train_loss,loss,acc,cal_acc,auroc,lr_auroc,lr_acc

[thejaminator]

i'll like to refactor this reporter functions so that they give back something like a EvalCSVResult.

from elk.training.reporter import EvalResult


class EvalCSVResult:
    layer: int
    train_loss: float
    eval_result: EvalResult
    # Only available if reporting baseline
    lr_auroc: Optional[float]
    # Only available if reporting baseline
    lr_acc: Optional[float]

and then another function does the responsbility of writing to a CSV / rounding to 4 d.p
but i'll do that in another MR :)

[AlexWan0]

Sounds good, could you make a new issue for this?

[AlexWan0]

Lgtm, thanks for the PR!