Metal chooses a buffer’s default storage mode based on the type of GPU
in use.
On Apple GPUs, the default mode is shared, which allows the CPU and GPU
to access the same memory without requiring explicit synchronization.
On discrete or external GPUs, Metal instead defaults to managed storage,
which does require explicit CPU–GPU memory synchronization.

This change aligns our buffer usage with Metal’s default behavior and
avoids unnecessary synchronization on Apple-silicon Macs. As a result,
memory usage on Apple hardware is reduced and performance improves due
to fewer sync operations.

Ref:
https://developer.apple.com/documentation/metal/setting-resource-storage-modes
Ref:
https://developer.apple.com/documentation/metal/synchronizing-a-managed-resource-in-macos

With the storage mode:

<img width="356" height="74" alt="image"
src="https://github.com/user-attachments/assets/e5a5bf9a-f339-417b-b5ab-818d8f692bd1"
/>

On main branch:

<img width="356" height="74" alt="image"
src="https://github.com/user-attachments/assets/6ccd77fe-7929-4423-9696-671d185ceffb"
/>

That's a 44% reduction of memory usage.

Release Notes:

- Reduced memory usage on Apple-silicon Macs by using shared memory
where appropriate

---------

Signed-off-by: Marco Mihai Condrache <52580954+marcocondrache@users.noreply.github.com>