Support Cython v3

[bjlittle]

( was formerly : "drop cython language_level on v3.0.0" )

📰 Custom Issue

Once cython 3.0.0 lands:

• drop use of the cython language_level compiler directive (3str will be the default behaviour)
  • explicitly set cython language_level #358
• add a min pin for cython>=3.0 for conda and PyPI deps
• address warning: #warning "Using deprecated NumPy API, disable it with " "#define NPY_NO_DEPRECATED_API NPY_1_7_API_VERSION" [-Wcpp], see
  • https://cython.readthedocs.io/en/latest/src/userguide/migrating_to_cy30.html?highlight=NPY_NO_DEPRECATED_API#numpy-c-api
  • https://cython.readthedocs.io/en/latest/src/tutorial/numpy.html?highlight=import_array#adding-types

See https://github.com/cython/cython/milestone/58

[pp-mo]

For avoidance of doubt, the cython 3.0 milestone (linked above) was closed Nov 2023 (!!)

[trexfeathers]

Currently struggling to get a current example of the NPY_1_7_API_VERSION warning - so that I can confirm I have successfully suppressed it! Due to log retention we no longer have any successful GHA examples, and when I build locally I don't get the warning.

Hoping #455 will produce what I need.

It did occur to me that NumPy might have removed the warning now that Cython has been around for a few months, but I cannot find any evidence of this:

• https://github.com/search?q=repo%3Anumpy%2Fnumpy+NPY_1_7_API_VERSION&type=pullrequests
• https://github.com/search?q=repo%3Anumpy%2Fnumpy+NPY_1_7_API_VERSION&type=issues

[pp-mo]

Closed by #460