metal : allow ops to run concurrently (#15929)
* metal : run graphs ops concurrently
ggml-ci
* cont : add flags for debugging and disabling concurrency
ggml-ci
* cont : refactor and handle fusing
ggml-ci
* cont : simplify - no need to use GPU address
ggml-ci
* cont : prepare mem ranges for reuse + add ggml-metal-common.cpp
ggml-ci
* cont : avoid redundant keywords in cpp [no ci]
* metal : reorder graph for better concurrency
ggml-ci
* metal : fix race on mem pool buffers
ggml-ci
* cont : add env GGML_METAL_GRAPH_OPTIMIZE_DISABLE
ggml-ci
* cont : refactor, optimize, add comments
ggml-ci
* cont : refactor ggml-metal.m
ggml-ci
* minor : update logs [no ci]
