allowing geometry to be fully made via constructor

[shimwell]

Hoping to contribute to @eepeterson mission of being able to entirely make the classes through the constructor. I thought I should have a go at allowing the geometry class to be specified through the constructor.

Checklist

• I have performed a self-review of my own code
  - [ ] I have run clang-format on any C++ source files (if applicable)
• I have followed the style guidelines for Python source files (if applicable)
• I have made corresponding changes to the documentation (if applicable)
• I have added tests that prove my fix is effective or that my feature works (if applicable)

I have added tests and run pytest with the pytest tests/unit_tests/test_geometry.py as the openmc.Geometry is the class that has been changed.

[paulromano]

For two parameters, this almost doesn't feel like it's worth it over just explicitly adding merge_surfaces and surface_precision

[shimwell]

I believe @eepeterson was keen on getting all the classes fully made from constructors as part of the repr, str and then xml to python code idea. But admittedly I could have misunderstood

[paulromano]

Sorry if I was not clear. I meant rather than adding the catch-all **kwargs as an argument, explicitly add merge_surfaces and surface_precision arguments. So @eepeterson's goal can still be attained.

[shimwell]

Ah sorry, you were clear I just miss read. I changed to explicitly adding these args

[eepeterson]

Thanks for starting this @shimwell! To follow on to @paulromano's comment: generally I think **kwargs should be used for pass through arguments to the superclass if necessary, whereas explicit keyword arguments are best for the class itself (especially if they are small in number).

[eepeterson]

Do we have a policy on how to write method/constructor signatures with type annotations yet? With type annotations (and default values in particular) I find this style a bit hard to read unless there are only 1 or 2 parameters. Since this line seems to be getting a bit longer than the 90ish rule, perhaps 1 argument per line, but I'd be curious to hear other perspectives. I think my preference is one per line with whitespace up the the ( but there are good arguments for other styles out there

[shimwell]

I've changed the code to multi line args and it does look better imo but I'm always keen automate this stuff and adopt whatever flake8 or black decides