CI fails - numpy version too high

[tomsail]

numpy just upgraded to version 2.0.0 and now make the tests in CI fail:

A module that was compiled using NumPy 1.x cannot be run in
NumPy 2.0.0 as it may crash. To support both 1.x and 2.x
versions of NumPy, modules must be compiled with NumPy 2.0.
Some module may need to rebuild instead e.g. with 'pybind11>=2.12'.

If you are a user of the module, the easiest solution will be to
downgrade to 'numpy<2' or try to upgrade the affected module.
We expect that some modules will need time to support NumPy 2.

Not only CI fails, but also new installs.
For new comers to be able to use this package, they would just have to

pip install numpy==1.26

at the end of the install.

I think we should downgrade to numpy<2 - we wouldn't recommend using it after a few releases anyway.

At the same occasion, I think it might be good to set up a proper pyproject.toml for new people to be able to install oceanmesh properly.

And also update the README accordlingly

[krober10nd]

Thanks for this. Can we make it compatible with numpy 2.0.0?