[Core] Separate header/source of Node. Also adding more documentation

[loumalouomega]

📝 Description

This PR refactors the Node class, primarily by reorganizing the code in the header (node.h) and implementing new functionality in the source file (node.cpp). The changes include:

1. Refactoring and Clean-Up:

   • Several unused imports and redundant definitions were removed from node.h.
   • The constructor and member functions were adjusted, with some deprecated or redundant code removed.

2. Move partially implementation to node.cpp

3. Node as final

4. Documentation:

   • New docstrings were added for various methods.

🆕 Changelog

• Removed unused includes and redundant code in node.h.
• Moved part of the code to source file.
• Improved function documentation for better clarity and maintainability.
• Node as final

[matekelemen]

I'd leave quite a few functions in the header.

[sunethwarna]

Since we are touching the Node here, why don't we make it final also? @KratosMultiphysics/technical-committee

[loumalouomega]

Since we are touching the Node here, why don't we make it final also? @KratosMultiphysics/technical-committee

Something tells me it is going to crash something

[roigcarlo]

I see no problem in the refactor but I doubt that for this particular class implementing something in the cpp can lead to any improvement. They are very cheap to parse anyway. The problematic ones (the inlined) still need to remain in the header.

That being said, why we want to make the node final exactly?