Remove restriction on NumPy v2

[awvwgk]

Closes #39

[awvwgk]

Using Mopac 23 I get all but one test passing, maybe there is a change in Mopac? But no problem with the newer NumPy.

=================================== test session starts ====================================
platform linux -- Python 3.13.2, pytest-8.3.5, pluggy-1.5.0 -- /home/sehlert/software/opt/conda/envs/pyberny/bin/python3.13
cachedir: .pytest_cache
rootdir: /home/sehlert/projects/git/mctc/pyberny
configfile: setup.cfg
collected 5 items                                                                          

tests/test_coords.py::test_cycle_dihedrals PASSED                                    [ 20%]
tests/test_optimize.py::test_optimize[ethanol] PASSED                                [ 40%]
tests/test_optimize.py::test_optimize[aniline] FAILED                                [ 60%]
tests/test_optimize.py::test_optimize[cyanogen] PASSED                               [ 80%]
tests/test_optimize.py::test_optimize[water] PASSED                                  [100%]

[awvwgk]

Jan @jhrmnn, could you have a look?