MAINT: numpy 2.0 support

[inoelloc]

Hello,
A pull request to support numpy 2.0

numpy-2-0-python-api-removals

• Alias np.string_ has been removed. Use np.bytes_ instead.
• Alias np.unicode_ has been removed. Use np.str_ instead.

numpy-2-0-c-api-removals

• npy_interrupt.h and the corresponding macros like NPY_SIGINT_ON have been removed.
  Need to include <signal.h> to avoid error: 'SIGINT' undeclared (first use in this function)

I am not sure if the python-package.yml workflow is still useful since the same tests are run inside build-wheels.yml

[smiet]

Should "oldest-supported-numpy" not be removed from the [build-system] in pyproject.toml.

at least it is unneccesary now with numpy 2.0 and the package is deprecated.

[jameskermode]

Thank you very much! I agree with removing oldest-supported-numpy from the dependencies. If you could do that then I'll go ahead and merge.

[inoelloc]

python 3.8 will no longer be supported by removing oldest-supported-numpy

[jameskermode]

OK, thank you, let's keep Python 3.8 compatibility.