Optimize elevation coverage service

[novalis]

Right now we're using a custom !UnifiedGridCoverage class to stitch together multiple TIF files for our elevation data. We should probably really be using an !ImageMosaic. The main reason we're not already is because the naive approach we're doing is roughly 200x faster than using the !ImageMosaic. I've emailed back and forth with Simone Giannecchini of the !GeoTools project who thinks we can optimize this:

I am pretty sure we can optimize this 'elevation service' even more.
As an instance you should supply a !GridGeometry2D to the reader and
also you should create it with the IGNORE OVERVIEWS hint in order to
get just a small area around the point you need.

Not a huge priority, but something it'd be nice to get to some day.

[abyrd]

We recently ran into elevation efficiency issues again. This old issue contains some hints on how that might be optimized.

[github-actions]

This issue is stale because it has been open 90 days with no activity. Remove stale label or comment or this will be closed in 30 days