Don't include std after module declaration

[n0F4x]

I tried compiling my project that uses modules but not the std module (FASTGLTF_USE_STD_MODULE is also turned off), but I get a compilation error (error: 'std::__promote::type' from module 'fastgltf.' is not present in definition of '__promote<_Args...>' provided earlier).
I presume this should be because the std headers are included after the fastgltf module declaration.
If not, this could be a Clang 19 bug. 🤷‍♂️