Create tests for turtle module

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
  • dot (see https://github.com/python/cpython/pull/138773)
• TurtleGraphicsError
• TurtleScreen
• TurtleScreenBase
• Vec2D

Some random notes:

1. For those going to work on teleport, see https://github.com/python/cpython/pull/107807#pullrequestreview-1584010411

Here, go the module's functions:

• Screen
• config_dict
• demo1
• demo2
• getmethpartlist (WIP: https://github.com/python/cpython/pull/135533)
• read_docstrings
• readconfig
• switchpen
• write_docstringdict

Linked PRs

• gh-138877

从 Lib/test/test_turtle.py 开始，检查 issue 中列出的未勾选公共类和函数，包括关于 teleport 和 getmethpartlist 的说明。在开始工作前确定一个聚焦的子集，并在该子集拥有覆盖其公共行为的有意义测试时视为完成。