Explore new performance syntax #2064
Description
The idea is detaching the references from extracting a performance variable. We need to make it easier for users to just extract performance variables without the strict need for a reference to check against. This is particularly relevant with libraries and reusable tests, where a reference is never known if the test is system agnostic.
This syntax should be in line with the new sanity syntax introduced with #2007 (using decorators, rather than assigning variables).
A prototype implementation can be found in this branch with the generic gpu_burn, and the cscs-specific gpu_burn checks.