Odd behavior for datasets with one epoch value

[bourque]

For dataset that have only one epoch value in it, loading the CDF via the cdf_to_xarray results in some unexpected behavior -- The epoch coordinates do not appear to be properly set in the resulting xarray dataset. The function throws a warning of ISTP Compliance Warning: epoch is listed as the DEPEND_0 for variable <variable_name, but the dimensions do not match., and the coordinates of the dataset will be listed as record0instead ofepoch`.

Having more than one epoch value appears to help avoid this issue, for example:

epoch = xr.DataArray(
    [time, time + np.timedelta64(1, "s")],
    name="epoch",
    dims=["epoch"],
    attrs=cdf_attrs.get_variable_attributes("epoch_attrs"),