Ignore warnings when compiletime.testing is imported

[som-snytt]

Fixes #23967

It needs more mechanism for compiletime ops that are inlined but not Inlined.

[som-snytt]

Another idea is that using the compile time facility makes all enclosing imports "used"; that results in false negatives instead of false positives.

Edit: in fact, all the warnings are nullified by the facility. We can't detect the erased usage of typeChecks, so just witnessing the import turns off linting the compilation unit.

The ultimate goal is to represent the typeChecks code as Inlined (by some convention).