Python helpers for common threading libraries (BLAS, OpenMP)

 Thread-pool Controls provides Python helpers to limit the number of threads
 used in the threadpool-backed of common native libraries used for scientific
 computing and data science (e.g. BLAS and OpenMP).
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 Fine control of the underlying thread-pool size can be useful in workloads
 that involve nested parallelism so as to mitigate oversubscription issues.