Adds Better Handling of reST/docstring Warnings

[mandli]

Before we were either ignoring build warnings or they were ending up in the docs. This PR adds a few new capabilities to better manage these:

• Ensure that warnings are not swallowed by the configuration
• Creates 3 new make build targets that help to check for build warnings (checkwarnings, checkwarnings-update, and checkwarnings-strict)
• Adds a baseline of warnings so that we know which ones are old and which ones are new
• Adds a mockup to deal with doc-strings that involve petclaw so we do not need to install a working copy to check those
• Adds a CI action to build and check against the "baseline" set of warnings that exist and fails if any new ones are added.
• Add some documentation on these changes to help find and update the baseline

Assisted-by: claude claude-opus-4-8