fix fmt include in Manager

[kwsp]

When building with -DKOMPUTE_OPT_USE_BUILT_IN_FMT=OFF using fmt from vcpkg, I was getting build errors in Manager.cpp saying error: no member named 'join' in namespace 'fmt'. join is defined in <fmt/ranges.h> which wasn't included. I'm not sure how kompute can build with the built in fmt.

Another trivial thing was that the <set> and <unordered_map> headers were not used in Manager.hpp so I moved them to Manager.cpp.

[kwsp]

This problem is blocking the vcpkg port of Kompute I'm working on

[axsaucedo]

Interesting, thank you for the fix @kwsp - LGTM

[kwsp]

I should mention that the fmt version downloaded by kompute in CMake is very old (8.x), while the current major release that VCPKG installs is 11.x. and the API might've changed. I think we should update the fmt downloaded by fmt in CMake too

[axsaucedo]

@kwsp I agree with you - I remember having a look at this but seeing some strange errors so ended up not prioritising, but certainly something I'd be up for if you were able to perform the update to latest