PythonOCC v7.8.1 upgrade

[JJMinton]

This PR updates pythonocc-core from v7.5.1 to v7.8.1.
This required

• updates to conda environment definitions
• replace removed .Nodes().Value(idx) functions with .Node(idx).
• Replace a number of functions with static methods to avoid deprecation warnings.

As a bonus, I have removed numerous unused imports.

[JoeLambourne]

This looks good.

I'm recommending updating the major version because we pull in a new PythonOCC which does force consumers to update OCC related code

[JJMinton]

I am getting failures around the read/write of shapesets. The interface was updated from .ReadFromString() to .Read(), as per this PR, but this is raising an error. I have opened an issue with pythonocc so will hold this for a while in hopes of getting a resolution.

[pradeep-pyro]

@JJMinton is this PR ready to merge?

[Late-March]

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[NarenR21]

Did this get merged? Would love to use 7.8.1 so that it doesn't break my other dependencies.

[Late-March]

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