Fix ZeroDivisionError in hull() for overlapping circles

[tairabun]

Summary

Sketch.hull() raises ZeroDivisionError when called on faces containing overlapping circles.

Reproducer:

from cadquery import Sketch, Location, Vector

Sketch() \
  .face(Sketch().circle(35).moved(Location(Vector(-19, 0, 0)))) \
  .face(Sketch().circle(35).moved(Location(Vector(19, 0, 0)))) \
  .hull()
# ZeroDivisionError: float division by zero

Traceback:

cadquery/hull.py:262, in arc_arc
    dx /= l
ZeroDivisionError: float division by zero

Root cause

When two circles overlap, boolean face fusion in Sketch.face() splits them into multiple arc segments. Arcs originating from the same circle share the same center point. When the gift-wrapping hull algorithm calls arc_arc() on two such concentric arcs, it computes l = distance_between_centers = 0 and then divides by l.

The hull algorithm was designed for one entity per circle. Multiple arcs per circle (from boolean fusion) violates this assumption.

Fix

Deduplicate arcs by center in convert_and_validate(), keeping one full-circle arc per unique center (with the largest radius). This ensures the hull algorithm sees exactly one entity per original circle, matching its design assumptions.

The fix is entirely in convert_and_validate() — no changes to the hull algorithm itself.

Test plan

• Added test_hull_overlapping_circles — hull via .push().circle().reset().hull()
• Added test_hull_overlapping_circles_equal_radii_via_face — hull via .face() composition
• Verified all 691 existing tests pass (full test suite)
• Verified the resulting hull face has positive area and can be used with .cutBlind() for 3D operations

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.15%. Comparing base (6cd5eeb) to head (d2b5d1c).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1989      +/-   ##
==========================================
+ Coverage   96.07%   96.15%   +0.07%     
==========================================
  Files          29       29              
  Lines        7956     7957       +1     
  Branches     1190     1191       +1     
==========================================
+ Hits         7644     7651       +7     
+ Misses        179      175       -4     
+ Partials      133      131       -2     

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