debugcommands: introduce standalone module for debug commands commands.py is our largest .py file by nearly 2x. Debug commands live in a world of their own. So let's extract them to their own module. We start with "debugancestor." We currently reuse the commands table with commands.py and have a hack in dispatch.py for loading debugcommands.py. In the future, we could potentially use a separate commands table and avoid the import of debugcommands.py.