Add CI test to check oversubscription and introspection in a numba prange loop with nested BLAS calls

[ogrisel]

numba can use several threading layers that should all be tested in CI:

https://numba.pydata.org/numba-doc/dev/user/threading-layer.html

[ogrisel]

Note #43 is required first to be able to test numba with its tbb threading layer.