Fix Read the Docs build: pin setuptools<82 for pkg_resources

setuptools 82.0.0 removed pkg_resources; the doc build and avocado.core
use it. Pin setuptools>=45.0.0,<82 in requirements-doc.txt and in
setup.py install_requires so docs build and all users get a working
setuptools until avocado migrates off pkg_resources.

Reference:
Assisted-By: Cursor-Claude-4-Sonnet
Signed-off-by: Harvey Lynden <hlynden@redhat.com>

Author: harvey0100

requirements-doc.txt

@@ -1 +1,3 @@
 sphinx-rtd-theme==2.0.0
+# Pin <82: setuptools 82.0.0+ removed pkg_resources (avocado.core still uses it at doc build time)
+setuptools>=45.0.0,<82

setup.py

@@ -509,5 +509,6 @@ def run(self):
             "plugin": Plugin,
             "test": Test,
         },
-        install_requires=["setuptools"],
+        # Pin setuptools<82: 82.0.0+ removed pkg_resources, which avocado.core still uses
+        install_requires=["setuptools>=45.0.0,<82"],
     )