Legacy editable install - switch to pyproject.toml

[sohang3112]

pip install -e . now shows this deprecation warning:

DEPRECATION: Legacy editable install of forth_kernel==0.3 from file:///home/sohangchopra/Programming/iforth (setup.py develop) is deprecated. pip 25.0 will enforce this behaviour change. A possible replacement is to add a pyproject.toml or enable --use-pep517, and use setuptools >= 64. If the resulting installation is not behaving as expected, try using --config-settings editable_mode=compat. Please consult the setuptools documentation for more information. Discussion can be found at pypa/pip#11457

See steps to fix