[FEA]: Implement concrete types that satisfy the resource concepts

[miscco]

This is an essential first step, but as-is, the interface isn't useful by itself and we need the following:

Concrete types that satisfy the resource and async_resource concepts

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1. [FEA]: Modularize <cuda/memory_resource> #1531
   feature request libcu++ +2
   
2. [FEA]: Implement a memory_resource using cudaMalloc and cudaFree #1512
   feature request libcu++ +2
   
3. [FEA]: Implement a memory_resource using cudaMallocManaged and cudaFree #1515
   feature request libcu++ +2
   
4. [FEA]: Implement a memory_resource using cudaMallocHost and cudaFreeHost #1516
   feature request libcu++ +2