[Bug]: CLI doesn't work without dev installation (pygambit)

[edwardchalstrey1]

What operating system are you using?

Linux

What version of draw_tree are you using?

0.4.2

What happened?

Unable to generate an image from a .ef file without pygambit being installed - this should work without pygambit which is an optional dependency:

draw_tree ocp.ef 
Traceback (most recent call last):
  File "/home/ed/projects/draw_tree/dtvenv/bin/draw_tree", line 5, in <module>
    from draw_tree.cli import main
  File "/home/ed/projects/draw_tree/dtvenv/lib/python3.12/site-packages/draw_tree/__init__.py", line 22, in <module>
    from .gambit_layout import gambit_layout_to_ef
  File "/home/ed/projects/draw_tree/dtvenv/lib/python3.12/site-packages/draw_tree/gambit_layout.py", line 1, in <module>
    import pygambit
ModuleNotFoundError: No module named 'pygambit'