Make decoder.py generic to the astronomical objects being rendered

[dereklhansen]

With the addition of the galaxy lensing to decoder.py, I think it makes sense to refactor Decoder._render_ptiles() to not hard-code each different object ("star", "galaxy", "lensed_galaxy").

bliss/bliss/models/decoder.py

Line 182 in 592d5eb

def _render_ptiles(self, tile_catalog: TileCatalog) -> Tensor:

I propose something like this:

    def _render_ptiles(self, tile_catalog: TileCatalog) -> Tensor:
        all_objects_list = []
        for renderer in self.renderers: #stars, galaxys, lensed_galaxies, etc
             centered_object_imgs = renderer(tile_catalog)
             objects_imgs = self.tiler.forward(tile_catalog.locs, centered_objects)
             all_objects_list.append(objects_imgs)
        return sum(all_objects_list)
    ...
    def __init__(...):
          self.renderers = []