[MacOS:] Metal.functional() wrongly returns true despite no GPUs available

[omlins]

The following tests were executed and failed because Metal.functional() returned true:
https://github.com/omlins/CellArrays.jl/actions/runs/11330323307/job/31507893740#step:6:564

[omlins]

@christiangnrd this is an issue somewhat similar to #453

[christiangnrd]

Thank you for taking the time to report these!

I'm not exactly sure what the best way to resolve this is.

We could enforce MTLGPUFamilyApple7 and MTLGPUFamilyMetal3 support through functional(), or we could add a new function like fully_supported() or something that only returns true if the device's GPU has the above support.

@maleadt @tgymnich Any thoughts?

[maleadt]

We could enforce MTLGPUFamilyApple7 and MTLGPUFamilyMetal3 support through functional(),

I think that would be the best option. Since we automatically select a device, without the user having to check if one is available and select it, it's fair to assume that code using said implicit device works after checking Metal.functional().

In CUDA.jl this is automatic, because the driver fails to initialize if no devices are available.