[$] Toward the unification of kselftests and KUnit

The kernel project, for many years, lacked a formal testing setup; it was
often joked that testing was the project's main reason for keeping users
around. While many types of kernel testing can only be done in the
presence of specific hardware, there are other parts of the kernel
that could be more widely tested. Over time, though, the kernel has gained
two separate testing frameworks and a growing body of automated tests to go
with them. These two frameworks — kselftests and KUnit — take different
approaches to the testing problem; now this
patch series from Thomas Weißschuh aims to bring them together.