Tentatively *deprecate* use_persis_return_sim/gen, zero_resource_workers, AllocSpecs.out

[jlnav]

We've worried for a long time that it's impossible to remove things without inconveniencing/warning users manually. For features/capabilities we'd like to remove or dramatically change, we ought to raise DeprecationWarnings for those features, warning of exactly when to expect changes.

I think nowadays users seem to be more likely to request new features, changes, or cleanups at the cost of complete backward compatibility. Plus, thankfully, we're not deleting old releases; I wouldn't mind releasing patches to old releases if requested, similarly to how Python 3.9, 3.10, etc. still get patches.

So based on a handful of conversations, I'll start by proposing the deprecation of those features listed in the title.