added ability to load stp files into a shape

[shimwell]

Proposed changes

This adds Shape().from_stp_file to the Shape class and makes use of this method in the Reactor.export_h5m_with_pymoab method.

This allows pymoab to be used as a method when making a reactor from a manifest.json file.

Previously this was only possible with the "trelis" method.

This means one can take a stp file(s) and run a neutronics simulation in the following manner ...

assuming you have a manifest.json like this

[
    {
        "stp_filename":"geometry.step",
        "material_tag":"my_material"
    }
]

import paramak, openmc

my_reactor = paramak.Reactor(
    shapes_and_components='manifest.json'
)

my_reactor.method = 'pymoab'

coords = openmc.stats.Point((0, 0, 0))
energy = openmc.stats.Discrete([1.41E7], [1.0])
source = openmc.Source(space=coords, energy=energy)

my_model = paramak.NeutronicsModel(
    geometry=my_reactor,
    source=source,
    materials={'my_material': 'eurofer'},
    mesh_tally_3d=['flux', 'heating'],
    mesh_3d_corners=[(-1, -1, -1), (1, 1, 1)]  # needed for now as the dimensions are not yet found automatically using this method
)

my_model.simulate()

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• 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

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• 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

If this is a relatively large or complex change, kick off the discussion by explaining why you chose the solution you did and what alternatives you considered, etc...

[shimwell]

Failing tests are unrelated and are being fixed in #830