Fix usage of apexpy in CI

[smithara]

Binary wheels for apexpy are not published because they are often failing when the build system is different from the user system. This makes it tricky to use in CI and for users to install SwarmPAL

Things to fix:

• Enable DSECS testing under Windows in Actions. Should be doable now by using https://github.com/smithara/actions_scratchpad/blob/main/.github/workflows/install_apexpy.yml#L35
• Clear up situation in readthedocs. Currently using fixed binary install from my own source:
  

  SwarmPAL/pyproject.toml

  Line 54 in b0f1b89

  "apexpy @ https://github.com/smithara/apexpy/releases/download/v1.1.0-binaries/apexpy-1.1.0-cp38-cp38-manylinux_2_17_x86_64.manylinux2014_x86_64.whl",

  
  (which PyPI rejects)
  - Configure readthedocs with compilers (haven't found a way to do this), so that apexpy can install from source
  - OR: Use a conda environment for the docs