Support for materials

[adrianschneider94]

Implemented material support.
In this approach, materials are stored in python dataclasses, the OpenCascade objects are only created when building the assembly.
Tests/docs are missing at the moment.

[shimwell]

This looks great, I wonder if there is ever a use case for a material to be a string in as an option in addition to these nice material classes you have here. I was wondering if something like this would be possible / useful

assy = cq.Assembly()
assy.add(cube, name="red_cube", material="steel")

[adam-urbanczyk]

@shimwell it would certainly be nice to have some predefined materials, and maybe allow to use the material name for other things too. But let's start with making CI green.

[codecov]

Codecov Report

Attention: Patch coverage is 96.44128% with 10 lines in your changes missing coverage. Please review.

Project coverage is 95.54%. Comparing base (8c68faa) to head (0f8b1d7).

Files with missing lines	Patch %	Lines
cadquery/materials.py	95.20%	4 Missing and 4 partials ⚠️
cadquery/occ_impl/assembly.py	97.26%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           master    #1815    +/-   ##
========================================
  Coverage   95.54%   95.54%            
========================================
  Files          28       29     +1     
  Lines        7319     7502   +183     
  Branches     1102     1131    +29     
========================================
+ Hits         6993     7168   +175     
- Misses        195      199     +4     
- Partials      131      135     +4     

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[adrianschneider94]

Material support in step exporting will get better in OCCT:
Open-Cascade-SAS/OCCT#447

[adrianschneider94]

This looks great, I wonder if there is ever a use case for a material to be a string in as an option in addition to these nice material classes you have here. I was wondering if something like this would be possible / useful

assy = cq.Assembly()

assy.add(cube, name="red_cube", material="steel")

Would probably nice to have a set of materials to get started, but I think, any real-world application will require custom material sets.
Maybe there's another solution and we can find an existing material repository that can be utilized.

(edit: for example https://physicallybased.info)

[adrianschneider94]

VRML export runs, but is not correct yet.