So many warnings

[jzwar]

Since the compiler got a bit more "pedantic", a lot of warnings are thrown during the build of splinepy on the c++ side.

Most of them are relatively unimportant and can be resolved by the compiler, however, it risks overlooking some relavant issues. As is good practice, we should try to get rid of these warnings asap.

[j042]

#54 !!!
I will see if I can do something about napf/nanoflann warnings