[cocopp] Declare pkg_resources dependency

Since Python 3.12, pkg_resources is not installed by default. We need to
explicitly pull in setuptools. This is a short term fix for #2229.

code-postprocessing/pyproject.toml

@@ -34,6 +34,7 @@ classifiers = [
 dependencies = [
   "matplotlib >=3.5.0",
   "numpy >=1.21.0",
+  "setuptools >=61.0", # For pkg_resources
 ]
 dynamic = ["version"]