Move CUDA support to CUDAExt

[IanButterworth]

Flux v0.14 makes CUDA.jl etc. support weak

This requires work to remove the CUDA array initialization in here.

[IanButterworth]

This is introducing an error and it's not clear why

     Testing Running tests...
┌ Info: The CUDA functionality is being called but
│ `CUDA.jl` must be loaded to access it.
└ Add `using CUDA` or `import CUDA` to your code.
prepareImage() input varieties: Error During Test at /Users/ian/Documents/GitHub/ObjectDetector.jl/test/prepareImage.jl:1
  Got exception outside of a @test
  MethodError: objects of type Nothing are not callable
  Stacktrace:
    [1] macro expansion
      @ Flux ~/.julia/packages/Flux/mqBbi/src/layers/basic.jl:53 [inlined]
    [2] _applychain(layers::Tuple{Nothing, Nothing, ObjectDetector.YOLO.var"#_act#16"}, x::Nothing)
      @ Flux ~/.julia/packages/Flux/mqBbi/src/layers/basic.jl:53
    [3] (::Flux.Chain{Tuple{Nothing, Nothing, ObjectDetector.YOLO.var"#_act#16"}})(x::Nothing)
      @ Flux ~/.julia/packages/Flux/mqBbi/src/layers/basic.jl:51
    [4] macro expansion
      @ Flux ~/.julia/packages/Flux/mqBbi/src/layers/basic.jl:53 [inlined]
    [5] _applychain(layers::Tuple{Flux.Chain{Tuple{Nothing, Nothing, ObjectDetector.YOLO.var"#_act#16"}}, ObjectDetector.YOLO.var"#_maxpool#19"{Int64}, Flux.Chain{Tuple{Nothing, Nothing, ObjectDetector.YOLO.var"#_act#16"}}, ObjectDetector.YOLO.var"#_maxpool#19"{Int64}, Flux.Chain{Tuple{Nothing, Nothing, ObjectDetector.YOLO.var"#_act#16"}}, ObjectDetector.YOLO.var"#_maxpool#19"{Int64}, Flux.Chain{Tuple{Nothing, Nothing, ObjectDetector.YOLO.var"#_act#16"}}, ObjectDetector.YOLO.var"#_maxpool#19"{Int64}, Flux.Chain{Tuple{Nothing, Nothing, ObjectDetector.YOLO.var"#_act#16"}}}, x::Nothing)
      @ Flux ~/.julia/packages/Flux/mqBbi/src/layers/basic.jl:53
    [6] (::Flux.Chain{Tuple{Flux.Chain{Tuple{Nothing, Nothing, ObjectDetector.YOLO.var"#_act#16"}}, ObjectDetector.YOLO.var"#_maxpool#19"{Int64}, Flux.Chain{Tuple{Nothing, Nothing, ObjectDetector.YOLO.var"#_act#16"}}, ObjectDetector.YOLO.var"#_maxpool#19"{Int64}, Flux.Chain{Tuple{Nothing, Nothing, ObjectDetector.YOLO.var"#_act#16"}}, ObjectDetector.YOLO.var"#_maxpool#19"{Int64}, Flux.Chain{Tuple{Nothing, Nothing, ObjectDetector.YOLO.var"#_act#16"}}, ObjectDetector.YOLO.var"#_maxpool#19"{Int64}, Flux.Chain{Tuple{Nothing, Nothing, ObjectDetector.YOLO.var"#_act#16"}}}})(x::Nothing)
      @ Flux ~/.julia/packages/Flux/mqBbi/src/layers/basic.jl:51
    [7] ObjectDetector.YOLO.yolo(cfgfile::String, weightfile::String, batchsize::Int64; silent::Bool, cfgchanges::Vector{Tuple{Symbol, Int64, Symbol, Int64}}, use_gpu::Bool)
      @ ObjectDetector.YOLO ~/Documents/GitHub/ObjectDetector.jl/src/yolo/yolo.jl:341
    [8] v3_tiny_COCO(; batch::Int64, silent::Bool, w::Int64, h::Int64, cfgchanges::Vector{Tuple{Symbol, Int64, Symbol, Int64}}, kwargs::@Kwargs{})
      @ ObjectDetector.YOLO ~/Documents/GitHub/ObjectDetector.jl/src/yolo/pretrained.jl:31 [inlined]
    [9] macro expansion
      @ ~/Documents/GitHub/ObjectDetector.jl/test/prepareImage.jl:2 [inlined]
   [10] macro expansion
      @ ~/Documents/GitHub/julia/usr/share/julia/stdlib/v1.11/Test/src/Test.jl:1577 [inlined]
   [11] top-level scope
      @ ~/Documents/GitHub/ObjectDetector.jl/test/prepareImage.jl:2
   [12] include(fname::String)
      @ Base.MainInclude ./client.jl:489
   [13] top-level scope
      @ ~/Documents/GitHub/ObjectDetector.jl/test/runtests.jl:7
   [14] include(fname::String)
      @ Base.MainInclude ./client.jl:489
   [15] top-level scope
      @ none:6
   [16] eval(m::Module, e::Expr)
      @ Core ./boot.jl:383 [inlined]
   [17] exec_options(opts::Base.JLOptions)
      @ Base ./client.jl:291
   [18] _start()
      @ Base ./client.jl:552
Test Summary:                  | Error  Total  Time
prepareImage() input varieties |     1      1  1.1s
ERROR: LoadError: Some tests did not pass: 0 passed, 0 failed, 1 errored, 0 broken.
in expression starting at /Users/ian/Documents/GitHub/ObjectDetector.jl/test/prepareImage.jl:1
in expression starting at /Users/ian/Documents/GitHub/ObjectDetector.jl/test/runtests.jl:7
ERROR: Package ObjectDetector errored during testing

[IanButterworth]

This works locally with FluxML/Flux.jl#2295