Cleaning out unused code and adding coverage

[john-science]

What is the change?

This is just a general cleanup PR.

1. Removed prepSearch(), which was fully deprecated years ago, and verified that it wasn't used anywhere downstream.
2. Removed a strange staticmethod SkippingXsGen_BuChangedLessThanTolerance, which was fundamentally unused.
3. Fixed the interactBOL test in DB interface to stop leaving test crumbs (FINALLY, this took like a year to find).
4. Moved two functions that were inside the FuelHandler.getAssembly() out of that function, to make them testable.
5. Added a ton some generic code coverage.

Why is the change being made?

I just ran afoul of the deprecated function, and wanted to do some cleanup.

---

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.

[albeanth]

If I could make 1 request, I know you grepped around, but please run this on the testing suite for an internal TP App before merging. Thank you, @john-science !

[john-science]

If I could make 1 request, I know you grepped around, but please run this on the testing suite for an internal TP App before merging. Thank you, @john-science !

I will do that, sure!

[john-science]

@opotowsky @albeanth Okay, I tested this downstream with the usual battery of cross-platform testing. It looks good!

[opotowsky]

@opotowsky @albeanth Okay, I tested this downstream with the usual battery of cross-platform testing. It looks good!

Merge away! 🚀