metal : allow ops to run concurrently (#15929)

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]