Following DM-31221, write a task that generates the highest-resolution HIPS-compatible coadds.

At first this task will rely on DM-33942 for the healpix dimensionality in the butler, and will not be able to generate a quantum graph; Jim Bosch assures me he can write some special code to generate the quantum graph.

The output of this task will be per-healpix, per-band coadds with the HPX wcs. Each coadd will be a full Exposure with an image, variance, and mask plane. A follow-up ticket will describe an afterburner task to output a proper HIPS directory tree with fits files containing only the image plane (though could be run to make a HIPS tree of variance or mask planes as well).