Use prebuilt XCFramework distribution of MLX

Hello,

Thank you for this valuable repository that consolidates the necessary resources. I am planning to switch to it.

Currently, when I'm building my AI app, it takes 75% of the time building MLX-related codes, which takes really long. I'm wondering if it is possible to build a variant that packs all the backend (MLX, llama.cpp, ...) into a single `.xcframework` that is static for linking. This would save many hours and computing time on Xcode Cloud.

And if you accept PR, I'd like to make one.

:)