Drops the module-local ``mm()`` helper in favour of the centralised
``ifcopenshell.util.unit.mm_to_m`` (added earlier in this PR). The
``as mm`` import alias preserves the existing call sites' readability.
Generated with the assistance of an AI coding tool.
Now we do not rely on small offset to keep using inner curves to create linings, if some part of the lining is not present (which happens on mullions and transoms) we'll create U or L shape extrusion instead of rectangle with inner curve.
Long story short - this should keep ifc for windows valid.
From this - https://i.imgur.com/hQuCcR3.png
To this - https://i.imgur.com/qZ2Lyfo.png
It's a bit hacky since we still use really small offsets to keep "The outer curve shall enclose all inner curves." rule for IfcArbitraryProfileDefWithVoids valid.
Also:
- refactored window modifier code - part of it is now reused building a door and can be used by other module in the future
- fixed bug with window lining intersecting frame when lining_depth < panel_depth
- simplified the way lining is built in ifc - previously it was using 4-6 extrusions, now it's 1-2 which is also better for 2D drawings
Gorgious56
