Add peer access support

[vzhurba01]

In a multi-GPU setting, right now it's not possible to memcpy directly between the two devices. A couple of checks would have to be done by cuda.core as part of enabling this:

• cuDeviceCanAccessPeer
• cuCtxEnablePeerAccess

[leofang]

This issue is actually very tricky because the modern way of exposing peer access support is again tied to the mempool/VMM APIs, such as cuMemPoolSetAccess/cuMemSetAccess, same as IPC (#103). We'll need a coherent, unified, and consistent solution here.