TorchStore singleton puts/gets

[allenwang28]

In pursuit of: #16

this will make it so that applications no longer have to create a MultiProcessStore and pass it everywhere:

from torchstore import MultiProcessStore

store = MultiProcessStore.create_store()

my_actor = spawn_actors(MyActor, store, ...)

instead any actor can simply call

import torchstore as store

store.put(...)
store.get(...)

[allenwang28]

note, you shouldn't need this if you hf auth login.

[casteryh]

I think it make more sense to do this in a submodule, so something like

from torchstore import torchstore as ts

instead of doing it at the top level.
Making this change should be trivial though.

[LucasLLC]

This idea was so great, and it came right in time because it made https://github.com/meta-pytorch/torchstore/pull/19 much easier. I'm closing in favor of that PR, but greatly appreciate the contribution!