Nurbs extensions

[adam-urbanczyk]

Quite some improvements for the NURBS module.

• direct visualization of Surface, Curve and their control points vis fig.show and show
• isoline construction
• isoline extraction matrix construction
• fixed off by one evaluation error for periodic curves and surfaces
• constrainedApproximate2D
• tests

[codecov]

Codecov Report

❌ Patch coverage is 99.31507% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 95.69%. Comparing base (8290128) to head (73a9998).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
cadquery/occ_impl/nurbs.py	99.20%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2019      +/-   ##
==========================================
+ Coverage   95.00%   95.69%   +0.69%     
==========================================
  Files          30       30              
  Lines        8742     9091     +349     
  Branches     1298     1357      +59     
==========================================
+ Hits         8305     8700     +395     
+ Misses        289      239      -50     
- Partials      148      152       +4     

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[jmwright]

@adam-urbanczyk I've restarted the MacOS CI job 4 times and it keeps failing. Restarting once or twice is normally enough.

[adam-urbanczyk]

Yup. For some reason mypy fails to start. I'll investigate.

[adam-urbanczyk]

I'll still investgate what's breaking with the newest mypy

[adam-urbanczyk]

Just in case: this PR is ready for review.

[jmwright]

Other than the comment made by @lorenzncode and the one comment I left about the if/elif logic, this looks good to me. Thanks @adam-urbanczyk !