Latency benchmark

Prerequisites:

uv pip install "cmake<3.28"

Install Xcode for extra dependencies related to metal to be installed.

Run the benchmark:

cmake core/src/benchmark -B benchmark_build
cmake --build benchmark_build --target benchmark_mlxfn -j10

# Benchmark latency:
./benchmark_build/benchmark_mlxfn ~/Documents/Magenta/magenta-rt-v2/models/mrt2_base