Added unit handling to STEP import and export

[jmwright]

@adam-urbanczyk @lorenzncode This fixes a long-standing issue where things are at the wrong scale when exchanging STEP files because CadQuery did not use OCCT's units mechanism.

[jmwright]

Related issues that should be closed after this is merged: #1829 #1449

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.01%. Comparing base (41445a2) to head (a9e4ab5).
⚠️ Report is 1 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2023   +/-   ##
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  Coverage   95.00%   95.01%           
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  Files          30       31    +1     
  Lines        8749     8765   +16     
  Branches     1298     1298           
=======================================
+ Hits         8312     8328   +16     
  Misses        289      289           
  Partials      148      148           

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[adam-urbanczyk]

Thanks for picking this up @jmwright , this is very needed! Could you also add another option to export (e.g. outputUnit : STEPUnitLiterals | None = None) that would control the output unit and make unit control the document unit too? The default behavior being document unit == output unit? Cf. xstep.cascade.unit and write.step.unit OCCT options.

[adam-urbanczyk]

More context: https://dev.opencascade.org/content/differences-behavior-units-xstepcascadeunit-and-stepcontrolwriter-75-76

[jmwright]

@adam-urbanczyk Is the current implementation that you had in mind?

[adam-urbanczyk]

Yes, thanks! Just give me some time to review.