tkinter can be a missing dependency

[buzmeg]

When attempting to use cli.py from a github checkout, I got a tkinter error:

% ./cli.py --help

+ /usr/bin/uv run --active -m dragonpy --help

Uninstalled 1 package in 18ms
Installed 95 packages in 233ms
Traceback (most recent call last):
  File "<frozen runpy>", line 189, in _run_module_as_main
  File "<frozen runpy>", line 148, in _get_module_details
  File "<frozen runpy>", line 112, in _get_module_details
  File "/var/home/foo/coco/DragonPy/dragonpy/__init__.py", line 9, in <module>
    from dragonpy.CoCo.machine import run_CoCo2b
  File "/var/home/foo/coco/DragonPy/dragonpy/CoCo/machine.py", line 17, in <module>
    from dragonpy.core.gui import DragonTkinterGUI
  File "/var/home/foo/coco/DragonPy/dragonpy/core/gui.py", line 17, in <module>
    import tkinter as tk
ModuleNotFoundError: No module named 'tkinter'

This, sadly, doesn't seem to be fixable from pip or uv. You may want to add something to flag that the end user will have to reinstall python with the tkinter module set up.

Thanks.