Raise error with unknown extensions.

[groutr]

Raise some sort of error when an unknown file extension is passed to read_file. This will avoid an unbound variable.

[kumdonoaa]

Great to always have this kind of checkpoint.

[groutr]

The building_forcing_sets in this same file function also has several issues. One thing I'm perplexed by is the assumption of a very specifically formatted glob string on L117 (https://github.com/NOAA-OWP/t-route/blob/master/src/troute-network/troute/hyfeature_network_utilities.py#L117).