`Const` is broken

`const_arrayref` calls `unsafe_cached_load`, which doesn't exist. We should probably fix this or just remove the code.
https://github.com/JuliaGPU/Metal.jl/blob/a8e6789406bfe5658c79ac76cafb10685359d5a9/src/device/array.jl#L92-L96

This is low priority since I don't think it's ever worked (KA's `@const` is not connected to this) but I opened the issue to keep track of it

Start in src/device/array.jl at lines 92-96 and inspect how const_arrayref calls unsafe_cached_load. Determine whether that code should be fixed or removed, since the issue leaves both options open. Done means const_arrayref no longer references the nonexistent function and its intended behavior is verified.

Written by the indexing model from the issue text.