[BUG] Epoch chart is rendered as a filled rectangle instead of a line

[Felrix]

Hi, I noticed an issue with how the epoch metric is displayed in the chart UI.

Expected behavior

The epoch chart should be rendered as a normal line chart, similar to other scalar metrics. Since epoch is logged as a scalar value over time, I expected it to appear as a line or points.

Actual behavior

The epoch chart is rendered as a large filled rectangle instead of a line and trackio only record last epoch.
However, the per-step train/loss chart is displayed correctly.

Screenshot

Code

for epoch in epochs:
    total_loss = 0.0

    for X, y in dataloader:
        loss = loss_fn(model(X), y)
        total_loss += loss.item()
        trackio.log({"train/loss": loss.item()}, step=epoch)

    avg_loss = total_loss / len(dataloader)
    metrics = {
        "epoch": epoch,
        "train/avg_loss": avg_loss,
    }
    trackio.log(metrics, step=epoch)