Add support for specifying GPU HW contexts

Currently RMTC has 2 contexts to simplify things: GPU & CPU. GPU is analogous to CUDA context in the system - however it would be better to be more specific, for example given a GPU context we could cycle through a system defined list of HW options with CUDA being one of them if required.

This would require exposure of the system object to multiple places - specifically when swapping contexts in Artifacts.

No files or tests are named. Start by tracing the current GPU and CPU context representations and the context-swapping paths in Artifacts, then determine how the system object can be exposed there. Done means GPU contexts can specify hardware options and cycle through the system-defined list, with CUDA available when selected.

Written by the indexing model from the issue text.