Creating a one-block test reactor to speed up testing

What is the change?

In this PR I created a test reactor from an existing single test block reactor:

armi/tests/smallestTestReactor/armiRunSmallest.yaml

Using this new test reactor in dozens of tests, sped up our unit tests by 25-30%!

Why is the change being made?

I am just trying to speed up our unit tests. (Close #1736)

On my personal laptop, I saw many unit tests go from between 2 or 6 seconds down to 0.1 to 0.2 seconds.

Perhaps more importantly, we now have the tooling to use across the ecosystem.

NOTE: Not all unit tests can use such a small reactor. Be design, if you are doing something like shuffling multiple assemblies, you can not use the smaller test reactor.

Checklist

[X] This PR has only one purpose or idea.
[X] Tests have been added/updated to verify any new/changed code.

[X] The code style follows good practices.
[X] The commit message(s) follow good practices.

[X] The release notes have been updated if necessary.
[X] The documentation is still up-to-date in the doc folder.
[X] The dependencies are still up-to-date in pyproject.toml.

terrapower / armi