Time misalignment between ERA5 and SARAH?

Version Checks (indicate both or one)

• I have confirmed this bug exists on the lastest release of Atlite.

• I have confirmed this bug exists on the current master branch of Atlite.

Issue Description

Hi,

I think there may be a time misalignment in the current implementation when working with instantaneous (satellite) data. As correctly written and considered (e.g. here: https://github.com/PyPSA/atlite/blob/master/atlite/datasets/era5.py#L173-L175), ERA5 takes as reference time the accumulated values of the last hour meaning 11:00 refers to 10:00-11:00.

Now, in the Sarah implementation you take the mean of the arrays at 11:00 and 11:30 and assign the time index of the first array (11:00): https://github.com/PyPSA/atlite/blob/master/atlite/datasets/sarah.py#L153-L156 which leads to the 1-hour time misalignment. See e.g. the spatially averaged values (GHI) for a June day :

So if I did not overlook anything and this bug is true, the only change required would be:
ds = ds.assign_coords(time=ds.indexes["time"] + pd.Timedelta(60, "m"))
after merging the data with the solar position (https://github.com/PyPSA/atlite/blob/master/atlite/datasets/sarah.py#L237)

I could fix this in the sarah3 compatibility pull request (https://github.com/PyPSA/atlite/pull/352) if required.

Reproducible Example

No response

Expected Behavior

No response

Installed Versions

Review atlite/datasets/sarah.py around lines 153-156 and 237, then compare the time handling described in atlite/datasets/era5.py around lines 173-175. Verify whether the merged SARAH time coordinate needs the proposed 60-minute shift, and confirm the June-day spatially averaged GHI values are aligned afterward.