Security and clarity improvements

[Bigfoot71]

I mainly added static to member functions where applicable, as well as noexcept to move constructors.

I also added the explicit keyword where preferable, while avoiding it in cases where the intent was clearly to facilitate logical conversions.

Additionally, I added the [[nodiscard]] attribute where appropriate, given that I also noticed the use of [[maybe_unused]] and thus assumed that the addition would be acceptable. This can always be removed if needed.

I also adjusted some inclusion issues that could prevent compilation depending on the order in which the headers were included, without directly including raylib-cpp.hpp.

There is also the addition of a few missing const qualifiers.

Finally, I made a few adjustments to constructors, avoiding initialization in the constructor body via set() where possible.

[RobLoach]

Thanks a lot 👍