added color to shape.export_stp using assembly

[shimwell]

Proposed changes

This adds color to the exported STP files. It makes use of the nice new assemblies feature by @adam-urbanczyk (thanks for that)

Exporting this manner also means that we also get an assembly tree instead of the flat list of solids we use to have so I will double check that the next stages of the workflow are compatible with that.

It is also possible to name parts of the tree. Unique names must be used so it appears one can't have the solid (blue cube) having the same name as the containing sub assembly (yellow) so I've appended an _ to the name of the subassemby

The use of compounds in assemblies also appears to not result in the color getting added to the stp file in CQ 2.1 (see the grey PF coils and divertors in screen shot)

Going to try a reactor soon

Types of changes

What types of changes does your code introduce to the Paramak? Put an x in the boxes that apply

• [ ] Bugfix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Code refactoring
• [ ] Documentation Update (if none of the other choices apply)
• [ ] New tests

Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your code.

• [ ] Pep8 applied
• [ ] Unit tests pass locally with my changes
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have added necessary documentation (if appropriate)

Further comments

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[codecov[bot]]

Codecov Report

Merging #804 (f3ddfdf) into develop (4e981a0) will decrease coverage by 0.03%. The diff coverage is 72.72%.

@@             Coverage Diff             @@
##           develop     #804      +/-   ##
===========================================
- Coverage    95.43%   95.39%   -0.04%     
===========================================
  Files           74       74              
  Lines         5252     5256       +4     
===========================================
+ Hits          5012     5014       +2     
- Misses         240      242       +2     

Impacted Files	Coverage Δ
paramak/reactor.py	91.86% <33.33%> (-0.24%)	:arrow_down:
paramak/shape.py	98.10% <80.00%> (-0.14%)	:arrow_down:
paramak/neutronics_utils.py	91.28% <100.00%> (ø)

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