unexpected behaviour plots.series_per_group

[HMEUW]

The plots.series_per_group function gives an unexpected behaviour.

https://github.com/ArtesiaWater/hydropandas/blob/2426022ead74875a5f5abf6830c405d07533e78c/hydropandas/extensions/plots.py#L740C20-L740C52

When only one column provided as by
When groupname is a string, than the filename is spoiled with - symbols, e.g. series_by_monitoring_well_group_P-B-4.png
When groupname is a float or int, the function fails.

My solution is to exclude this line.

When a list is provided as by
You expect something as the join function. Therefore 2 lines up, include: groupname = '-'.join(str(x) for x in groupname)

Maybe I missed something in the function logic. Otherwise, I will fix this issue.