Make staging optional

The content of the staging chapter is pretty much the same as it was in the original tutorial. But that was written at a time where (Re)BAR/SAM where not a thing on desktop.

But with pretty much desktop GPU now offering a device local + host visible memory type just like unified architectures (iGPUs, Mobile), staging is now mostly no longer necessary. At least not for buffers.

We should update the staging chapter accordingly.

That chapter also seems to have outdated information (limit of 4096 memory allocs on nvidia), that needs to be updated too.

Open the staging chapter and review its explanation of when staging is needed for buffers, especially on desktop GPUs with device-local and host-visible memory. Verify the chapter's statement about the NVIDIA memory-allocation limit against current information. Done means the chapter reflects current guidance and removes or updates outdated claims.

Written by the indexing model from the issue text.