[WIP] Initial implementation b-spline/nurbs tools

[adam-urbanczyk]

• Basic NURBS book algorithms
• Sparse design matrix
• Sparse periodic design matrix
• Sparse derivative matrix
• Sparse periodic derivative matrix
• Discrete penalty matrix
• Conversion to/from OCP
• Approximation
• Periodic approximation
• Loft
• Loft with constraints

[codecov]

Codecov Report

Attention: Patch coverage is 20.23121% with 138 lines in your changes missing coverage. Please review.

Project coverage is 93.95%. Comparing base (f07e7e0) to head (97fef3f).

Files with missing lines	Patch %	Lines
cadquery/occ_impl/nurbs.py	20.23%	138 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1859      +/-   ##
==========================================
- Coverage   95.66%   93.95%   -1.72%     
==========================================
  Files          28       29       +1     
  Lines        7431     7604     +173     
  Branches     1122     1150      +28     
==========================================
+ Hits         7109     7144      +35     
- Misses        193      331     +138     
  Partials      129      129              

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