Continuous Integration Testing

[jeremylt]

I see a job here for building the paper, but not for running the test suite:

https://github.com/jeremiah-corrado/fem_2d/tree/main/.github/workflows

actions-rs provides a wide range of good GitHub actions for testing and code coverage that make CI fairly painless.

I recommend including a CI job for running your crate test suite. I would also consider using Tarpaulin, possibly in CI, to explore areas where bugs may be hiding in your code due to low or no testing of various functions.

[jeremiah-corrado]

@jeremylt I've set up CI testing for pushes/pull-requests into the main branch. Its currently set up to check for build errors, and run all of the doc/unit tests (except it does skip the slepc_problem unit-test because it relies on the external slepc solver).