Fixed issues to move to Inventree 1.2.3 and small bug fixes

[dwelting]

• Fixed some API issues for the newest Inventree API.
• Fixed a small Kicad symbol writer bug where it couldn't parse the omega (Ω) symbol.
• Made Flet version 0.24.1 the default for now, because the newest versions don't support the currently used decorators.

This all made it possible to:

1. Use Ki-ntree setup_inventree to setup the categories and parameters
2. Add a part to Inventree 1.2.3 and Kicad 9.0.8, using python 3.13.

[T0jan]

@dwelting ah nice, was just about to fix these issues myself, I will merge this and will deal with the problems in the workflows in my branch