Fix numpy v2 breaking changes

[fjosw]

The upcoming numpy v2.0.0 release introduces a few breaking changes for autograd. This PR fixes these issues:

• msort was removed from the numpy API. I added conditional imports. The corresponding VJPs are now only defined if the numpy version is <2.
• np.array(value, copy=False) was removed. The same effect can now be achieved via np.asarray(value).
• The broadcasting rules for np.solve changed.
• np.linalg.linalg was renamed to np.linalg._linalg.

One thing that I did not adress in this PR is the changing behavior for np.sign with complex arguments. Instead of the sign of the real part, numpy now returns z /|z|.

On my machine all tests pass with the latest release versions (numpy==1.26.4 scipy==1.12.0) and the current release candidates (numpy==2.0.0.rc1 scipy==1.13.0rc1) but for tests/test_systematic.py::test_sign which fails for numpy v2 with

tests/numpy_utils.py:37: in unary_ufunc_check
    check([comp, matc])
autograd/test_util.py:77: in _combo_check
    _check_grads(fun)(*_args, **dict(_kwargs))
autograd/wrap_util.py:20: in nary_f
    return unary_operator(unary_f, x, *nary_op_args, **nary_op_kwargs)
autograd/test_util.py:56: in check_grads
    check_jvp(f, x)
autograd/test_util.py:43: in check_jvp
    check_equivalent(jvp(x_v)[1], jvp_numeric(x_v))
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

x = array(0.+0.j), y = np.complex128(-0.2141399934041388+1.070699966299049j)

because of the aforementioned changes to the behavior of the sign function.

[j-towns]

Thanks for this @fjosw. I will try to take a look at some point in the next couple of weeks.