Update cython extensions to make them `free-threading` compatible

[kif]

Resources: https://py-free-threading.github.io/porting-extensions/#__tabbed_1_2

• Either comment with: cython: freethreading_compatible = True
• Or patch the program globaly in meson:

cy = meson.get_compiler('cython')
if cy.version().version_compare('>=3.1.0')
    add_project_arguments('-Xfreethreading_compatible=true', language : 'cython')
endif