Mac OS: Bringing metal support

[baileyheading]

Work is underway to get metal working for this project. Keen to get help from anyone interested.

TODO:

• [ ] add conv_tranpose_1d for metal (already has cpu implementation)
• [ ] modify ggml_pad backend and added ggml_pad_ext for metal
• [ ] add pad_reflect_1d to metal (already has cpu implementation)
• [ ] add unfold_1d to metal (already has cpu implementation)

Existing PRs from @balisujohn decent example to follow for the changes done to CUDA already: https://github.com/ggerganov/ggml/pulls/balisujohn