add basic CI

[Sladuca]

Problem

We don't yet have CI.

Solution

Set up a very basic CI pipeline with GHA that we will expand later. For now, it on every PR, it will:

1. spin up a container with rust dependencies installed
2. do cargo test

Tasks

to-do list of things that need to happen in order to implement said solution

• set up GHA
• write GHA yml telling it how to test cargo test