turtle module has too few tests.

These are the module's public classes to review if there are test and/or implement them:

• RawTurtle
• ScrolledCanvas
• TNavigator
• TPen
• Tbuffer
• Terminator
• Turtle
• TurtleGraphicsError
• TurtleScreen
• TurtleScreenBase
• Vec2D

Some random notes:

1. For those going to work on teleport, see gh-107805: Fix signatures of module-level generated functions in turtle #107807 (review)

Here, go the module's functions:

• Screen
• config_dict
• demo1
• demo2
• getmethpartlist (WIP: [WIP, do not merge] add TestGetmethparlist test to getmethparlist #135533)
• read_docstrings
• readconfig
• switchpen
• write_docstringdict