GeezerVison

Summary

Addresses #144338 by improving the cmd.Cmd documentation to make the emptyline() and do_EOF patterns more discoverable:

• Add a note to cmdloop() docs that do_EOF should be defined to handle Ctrl-D/EOF gracefully, with a cross-reference to the example
• Add a practical tip to emptyline() docs about overriding with pass to suppress the default repeat-last-command behavior
• Add emptyline() and do_EOF() methods to the existing TurtleShell example to demonstrate these common patterns

These are the two most commonly needed overrides that new cmd.Cmd users struggle to discover from the current documentation.

Closes #144338

Test plan

• Documentation builds without warnings
• Example code in docs is syntactically correct

• Issue: Add a tutorial for cmd.Cmd for emptyline() and do_EOF #144338

📚 Documentation preview 📚: https://cpython-previews--145292.org.readthedocs.build/