update mkl_umath to align it with numpy-2.*

[vtavana]

In this PR, mkl_umath is aligned with numpy-2.*. The changes include:

1. the definition of numpy.sign for complex number is updated in numpy-2.*, mkl_umath is modified accordingly.
2. documentation for ufunc is updated. Now we have two documentation files which are borrowed from NumPy one is for numpy-1.26.4 and the other one for the most recent version of NumPy, i.e. numpy-2.2.5.
3. In both numpy-1.26.4, and numpy-2.2.5, true_divide is an alias of divide. The same change is made in mkl_umath. Previously, divide was an alias of true_divide.
4. generate_umath.py is updated to align with numpy-2.2.5.
5. new workflows are added to build and test the package with both numpy<2 and numpy>=2.

[ndgrigorian]

@vtavana
should we add conditional definition based on if NumPy > 2? Since we still are supporting 1.26.4

[vtavana]

@vtavana should we add conditional definition based on if NumPy > 2? Since we still are supporting 1.26.4

@ndgrigorian Yes, I am planning to do it. The PR is a draft and not finalized yet