Make it possible to eager load spatial cache

[njakobsen]

When indexing in glint, it'd be helpful to be able to eager load the spatial cache to avoid thousands of queries like this:

SpatialCache Load (0.4ms)  SELECT  "spatial_caches".* FROM "spatial_caches" WHERE "spatial_caches"."spatial_model_id" = $1 AND "spatial_caches"."spatial_model_type" = $2 AND "spatial_caches"."intersection_model_type" = 'Site'  ORDER BY "spatial_caches"."id" ASC LIMIT 1  [["spatial_model_id", 224037], ["spatial_model_type", "Encumbrance"]]

The complication is that there is an association for spatial cache, but we're adding a model type query to the end, so it can't use the eager loaded association.