Refactor Ray class into its own file

[GuySten]

Description

Currently, the cpp Ray class is located at plot.cpp.
I intend to use this class for the point detector feature.
This PR move this class into ray.cpp because this class is useful for general ray tracing and not solely for plotting.

Checklist

• I have performed a self-review of my own code
• I have run clang-format (version 18) 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)

[vitmog]

@GuySten Extracting Ray is useful, in my opinion. Do you see an overlap of your plans with #3833?

[GuySten]

Yes, I intend to create a subclass of Ray with the functionality in that issue for point detector purpose.