Investigate and improve `numba` back-end

[redeboer]

• See https://stackoverflow.com/a/65090938
• Use nopython=True instead of forceobj=True
  

  tensorwaves/src/tensorwaves/function/_backend.py

  Line 74 in b7a4efd

  return partial(numba.jit, forceobj=True, parallel=True)