Use pinned memory for doing transfers

[Corey Lowman]

[Eric Christiansen]

Hey, just to be clear, you mean something like RustaCUDA's LockedBuffer, right?

FYI I need this to switch from RustaCUDA to cudarc.

[Corey Lowman]

Yep, this will be utilizing cuMemAllocHost and cuMemFreeHost underneath the hood, which is also what the LockedBuffer is using.

As far as how this would be integrated into result/safe APIs, we could either:

1. Have a separate htod copy method for pinned transfers (htod_pinned_copy)
2. Change the existing htod_copy methods to accept something like AsRef<[T]> and make sure we can implement that trait for the page locked memory.