Add rectangular HVAC duct reductions

[gitgrahamdunn]

Summary

• adds rectangular HVAC duct transitions/reducers for the Add HVAC duct support -> Reduction roadmap item
• adds a new DuctReduction parametric object with editable inlet/outlet width and height, wall thickness, transition length, and outlet offsets
• adds DuctReduction_Rectangular.csv with concentric and flat-bottom rectangular transition presets
• adds an Insert duct reduction command/form and wires it into the piping toolbar
• marks the HVAC Reduction roadmap item complete

Source Data

• Transition lengths are sized from a 15-degree maximum side taper rule, using the ductwork transition guideline basis from Northwestern 23 3114 - Ductwork: https://www.northwestern.edu/facilities/docs/construction/design_guidelines/23_hvac/NU_23%203114%20-%20DUCTWORK.pdf
• CSV rows store inlet/outlet dimensions, wall thickness, length, offsets, and source URL for auditability.

Preview

Validation

• python3 -m py_compile pFeatures.py pCmd.py pForms.py CPipe.py InitGui.py Quetzal_tooltips.py
• git diff --check
• CSV integrity check for 12 rows and <=15.1-degree side taper mapping
• FreeCAD command-mode construction check for direct DuctReduction and pCmd.makeDuctReduction: both produced one solid with nonzero volume and two ports