* - create a gpu metrics (internal) registry
- the objective is to separate the cpu and gpu implementations such that they evolve
indepedently. to that end, this approach will:
- preserve the same metrics configuration (from the end user perspective)
- internally delegate the responsibility to the gpu metrics builder when there is a
valid device present
- decouple the gpu metrics builder from the cpu ones to prevent misuse
- move away from including the cuda file from within the cc file and segregate the code
via ifdef's
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