Add setuptools version constraint in requirements.txt

[andrew-c-ross]

Read the Docs builds started failing March 5 with:

python -m sphinx -T -b html -d _build/doctrees -D language=en . $READTHEDOCS_OUTPUT/html
Traceback (most recent call last):
  File "<frozen runpy>", line 198, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "/home/docs/checkouts/readthedocs.org/user_builds/cefi-regional-mom6/envs/latest/lib/python3.11/site-packages/sphinx/__main__.py", line 13, in <module>
    from sphinx.cmd.build import main
  File "/home/docs/checkouts/readthedocs.org/user_builds/cefi-regional-mom6/envs/latest/lib/python3.11/site-packages/sphinx/cmd/build.py", line 26, in <module>
    from sphinx.application import Sphinx
  File "/home/docs/checkouts/readthedocs.org/user_builds/cefi-regional-mom6/envs/latest/lib/python3.11/site-packages/sphinx/application.py", line 42, in <module>
    from sphinx.registry import SphinxComponentRegistry
  File "/home/docs/checkouts/readthedocs.org/user_builds/cefi-regional-mom6/envs/latest/lib/python3.11/site-packages/sphinx/registry.py", line 22, in <module>
    from pkg_resources import iter_entry_points
ModuleNotFoundError: No module named 'pkg_resources'

setuptools version 82.0.0, released Feb 8 2026, removed pkg_resources (https://setuptools.pypa.io/en/latest/history.html#v82-0-0)

This PR adds setuptools<82.0.0 to requirements.txt to attempt to fix this.

[andrew-c-ross]

This does build successfully on my local machine

[uwagura]

I wanted to run this in my workstation, but I ran into issues with doxygen. In any case, it's a pretty minor change that is documented on the setuptools website, so I think we can go ahead and merge it in