[REF] Ensure the [[nodiscard]], [[maybe_unused]] or any other specifiers are used when possible

[AndreasLrx]

Describe the request

• Every getter should be [[nodiscard]], and also any method which doesn't change the object itself but returns a value instead
• Unused function parameters (for example in virtual method) should be [[maybe_unused]]
• Functions must have noexcept if possible.

Describe the needs

This will allow some compilers optimization as long as a better code comprehension/coherence.

It should have been written since the beginning of the project but I wasn't aware of these specifiers at the time.