Set threadsafe behavior for numba parallelism
- xref #https://github.com/numba/numba/issues/6839#issuecomment-867977583
- [x] tests added / passed

Applicable for 1.3.0 since this behavior can appear for the new `method="table"` feature for rolling/expanding

cc @jbrockmendel 

With this i don't get segfaults, but am getting test failures > With this i don't get segfaults, but am getting test failures

Which ones in particular? > Which ones in particular?

All of the test_table_method_rolling_methods tests Got it. Might not be the best thing to hardcode a particular threading backend for numba either. I'll just document this in another PR. 