Moving FuelHandler Algorithms to separate files

[john-science]

Description

The FuelHandler.py file has a ton of algorithms of various kinds that are very specific to hex assembly reactors. This has caused lots of confusion for people who are implementing some sort of fuel handling logic. It also muddies the waters significantly between general fuel handling logistics code and detailed hex assembly algorithms.

The code in the old fuelHandler.py has been broken up into three files:

• fuelHandlers.py - has FuelHandler class
• hexAssemblyFuelMgmtUtils.py - Assorted shuffling and misc algorithms for managing hex assembly reactors.
• assemblyRotationAlgorithms.py - Rotation algorithms called by FuelHandler.outage(). (This does seem to be specific to assembly/hex-assembly reactor, but FuelHandler.outage() will only call it if a particular setting is used, which does an okay job of keeping the FuelHandler class from being specific to hex assemblies.)

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Checklist

• This PR has only one purpose or idea.
• Tests have been added/updated to verify that the new/changed code works.

• The code style follows good practices.
• The commit message(s) follow good practices.

• The release notes (location doc/release/0.X.rst) are up-to-date with any bug fixes or new features.
• The documentation is still up-to-date in the doc folder.
• The dependencies are still up-to-date in setup.py.

[keckler]

It makes a lot of sense to move those fuel handler methods off of the class anyways, or at least to make them into staticmethods, because none of them utilized the class/instance attributes at all.