Set up github CI workflows

[dodexahedron]

What it says on the tin.

Setting up standard CI workflows for building, testing, and deploying.

[dodexahedron]

There's a mostly default CodeQL workflow in already, which I set up while setting up the project.

It most likely will continue to fail until I'm closer to finishing #2

[dodexahedron]

The CodeQL workflow got nuked by a change I made earlier.

It has been restored and appears to be doing its thing, at the moment...

[dodexahedron]

Well, I suppose I can at least set most of this up before #3 can move forward - just not the deploy to nuget obviously.

I'll set up build and test workflows since those aren't really dependent on it.

[dodexahedron]

This actually prompted a review and revamp of our internal workflows.

What I'm going to do is take those and just cherry-pick the parts of that I feel are at least nice to have over here, because most of those are significant overkill for this repo.