llama.swiftui : add bench functionality (#4483)
* llama.swiftui : add bench button
* llama.swiftui : initial bench functionality
* force to use n_gpu_layers on simulator
* add download buttons & expose llamaState.loadModel
* update project.pbxproj
* comment #Preview & fix editorconfig check
* gitignore : xcode stuff
* llama.swiftui : UX improvements
* llama.swiftui : avoid data copy via "downloadTask"
* llama.swiftui : remove model from project
* llama : remove "mostly" from model infos
* llama.swiftui : improve bench
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Co-authored-by: jhen <developer@jhen.me>
