Move costs under a manager

[timothy-nunn]

Consolidate findings stellarator-2 that the PROCESS call order is wrong and the understanding that the a custom cost model won't be instantiated until after the models have been loaded. A manager class will allow both of these changes to coexist.

[timothy-nunn]

Cost manager cannot be made transparent, will keep as it currently is while modifying the init order (#3121) and I will work with @j-a-foster to resolve his issues with model injection.