improve SVG import color hadling

[snoyer]

I fixed a bug in ocpsvg regarding shapes declared as filled in an SVG document but that cannot be imported as faces, for example a single line segment. That included a better method to retrieve the correct color based on the imported OCP shape type.

This PR changes the SVG importer to use the new color_for(shape) method.
The behavior should be functionally identical except for aforementioned degenerate cases. I mostly want to push this change so build123d doesn't break when I deprecate the previously used color property from ocpsvg.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6389aa3) 95.80% compared to head (10b4448) 95.81%.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #366      +/-   ##
==========================================
+ Coverage   95.80%   95.81%   +0.01%     
==========================================
  Files          23       23              
  Lines        7143     7144       +1     
==========================================
+ Hits         6843     6845       +2     
+ Misses        300      299       -1     

Files	Coverage Δ
src/build123d/importers.py	97.46% <100.00%> (+0.03%)	⬆️

... and 1 file with indirect coverage changes

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