Allow setup.py --version to run without Cython, numpy

[taldcroft]

Description

This addresses the problem in sot/skare3#255.

See sot/chandra_time#40 for more details of functional testing (environment setup and commands).

Testing

• Passes unit tests on MacOS
• Functional testing
  • setup.py --version gives expected output in a minimal env (no Cython, no numpy)
  • setup.py build_ext --inplace fails in the minimal env with an import error
  • setup.py test builds and passes in a ska3 env

[javierggt]

To expand on my comment:

• The current setup requires that we have cython in the conda build environment just to get versions. If not, we get an error.
• The setup after this PR would require any user to have cython in their environment at the moment this is installed. If not, there will be no warning and you get a crippled package.

Of the two, I prefer the first one. It is limited to us and there is no silent unintended consequence. It is not hard to include cython in our build environment.

Is there no other way around?

[taldcroft]

@javierggt - good catch. The only thing I can think of is special-casing --version by checking sys.argv[1] for that string. There are a bunch of other informational commands and this gets ugly catching them all, but we can at least remove the need for cython in the ska_builder.py environment with the one check.

[javierggt]

Something like checking the --version argument could be. Ugly but I think would work.

[taldcroft]

@javierggt - I changed the logic here and in chandra.time, please have a look.

[javierggt]

It seems fine to me

[javierggt]

Wouldn't something like this then silently not install the extension if you install within an environment that does not have cython?