Add 3.14 testing to CI and fix one 3.14 issue

[braingram]

I was able to successfully run the python unit tests with python 3.14. I noticed one warning:

galsim/setup.py:1369: SyntaxWarning: "\." is an invalid escape sequence. Such sequences will not work in the future. Did you mean "\\."? A raw string is also an option.
  vi = re.split('\.|-',galsim_version)

This PR fixes the above invalid escape (#1335 also fixes the same regex in the same way) and adds 3.14 to the CI.

Is main the correct branch to target for these changes?

Also if this warrants a changelog entry please let me know where to add one. Thanks!

[rmjarvis]

Thanks Brett. There are some other fixes on #1335 that would be needed to get the CI to pass here. So rather than port them over, I just added the 3.14 addition to that PR. So I'm closing this one. But thanks for checking that everything works fine in 3.14.

[braingram]

Thanks!