[Feature]: Smart default for parallelism

[MilesCranmer]

Feature Request

It would be nice to have parallelism be set in a smart way (parallelism="auto"), rather than always set to "multithreading". For example:

1. deterministic == True => parallelism="serial"
   • We could also forward the global numpy random seed, if the user does not provide a random state?
2. numprocs is not None => parallelism="multiprocessing"
3. cluster_manager is not None => parallelism="multiprocessing"

And in also other cases, we default to "multithreading".