Add in-source Tracy profiler

[foxtran]

This patch adds support of Tracy profiler on hot-path of GFN2 method. I did not profile everything, but the most interesting parts are covered. Anyway, there is a room for optimizing and for more profiling. Have fun! 🎉

Only CMake build system is supported. Tested with GCC and Intel LLVM compiler sets.

[foxtran]

@awvwgk, what is minimum supported version of GCC? Do you keep some version that must compile xtb always?

[foxtran]

@thfroitzheim, what is about in-source profiler? :-)

[thfroitzheim]

For this to be practically usefull for more people than you, we need some kind of documentation on how to use it (maybe a short in the Readme and then a detailed explanation similar to the install instructions for meson and cmake).