Update for cython 3

[mcflugen]

This is a small pull request that updates the cython code to work with cython 3. All that was done was to add noexcept to a couple of the functions. This fixes two compile errors.

plume/ext/centerline.pyx:140:17: Cannot assign type 'double (*)(double, void *) except? -1 nogil' to 'double (*)(double, void *) noexcept nogil'. Exception values are incompatible. Suggest adding 'noexcept' to type 'double (double, void *) except? -1 nogil'.

[mcflugen]

I also had to set PYTHONIOENCODING="utf-8" for the CI to avoid a unicode encoding error on Windows. This error is likely the result of the LANG environment variable not being set (see Textualize/rich#212).