[cudapoa] Update cudapoa to use DeviceAllocator

[atadkase]

• Adds DeviceAllocator as default allocator for caching device allocations.
• Updated size limit to be a int64_t everywhere.

[r-mafi]

@atadkase, looks like 4 out of 29 tests fail. Have you checked if they run locally on your machine? I reviewed and the changes look good.

[atadkase]

rerun tests