Use package extensions

[mcabbott]

Julia 1.9 should allow this package to remove the use of Requires here:

https://github.com/mcabbott/Tullio.jl/blob/master/src/eval.jl#L36-L64

More ambitiously, it could also allow the present checks by the macro of whether LoopVectorization or CUDA exist in the calling scope to be replaced with something more principled.

[KristofferC]

This would indeed be nice. Tullio.jl is one of the worst packages when profiling loading https://github.com/JuliaComputing/OmniPackage.jl when it comes to time spent in __init__ right now due to the heavy use of Requires.jl (approx 0.5 seconds spent in it).