indexed fits reader and angle unit conversion for LSST refcat style catalogs

[psferguson]

I am converting an lsst style refcat to hats format.
The lsst style is 131_073 htm7 shards in fits format.
Additionally the coord_ra/dec columns are in radians not degrees

I managed to get something working, but I ran into dask issues when I tried to make my own reader to do the unit conversion.

I imagine it could be useful to specify the ra/dec column units, and an indexed reader for fits (like parquet/csv) would be nice.

[hombit]

Related to #378

[dougbrn]

Thanks for the issue @psferguson ! In the short term if you are still having any dask difficulties, let me know, I would be happy to help try to troubleshoot.

[psferguson]

Thanks @dougbrn I managed to find a functional but bad workaround this time.
I did the unit conversions and converted the many small fits files to larger parquet files prior to importing the catalog.
This let me just run the hats_import pipeline sucessfully