Coefficient px,py,pz planes

[psauvan]

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Description

Change way of writting parameters of PX, PY, PZ planes in output files. Instead of evaluating the parameter as the scalar product of the plane normal with a point on the plane, the x,y,z component of the plane is used.
This should fix some error when model dimensions are large.

Fixes issue

Please link to any issues that this PR fixes

Checklist

• I'm making a PR from a feature branch on my fork into GEOUNED-org/GEOUNED/dev branch
• I have followed PEP8 style guide for Python or run a formatter such as black or ruff format on my code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works