Pin setuptools to avoid mlflow import failure (pkg_resources missing)

[samdporter]

mlflow==2.10.0 imports pkg_resources, but our environment currently resolves setuptools to latest, where pkg_resources may be unavailable. This causes:
ModuleNotFoundError: No module named 'pkg_resources'

Easy fix is to add setuptools<81 to requirements.txt

This triggers a deprecation warning:

UserWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html. 
The pkg_resources package is slated for removal as early as 2025-11-30. Refrain from using this package or pin to Setuptools<81.
  import pkg_resources  # noqa: TID251

But works fine