`std.testing.fuzzInput`: ability to choose whether timing out is considered a fail or a pass

[andrewrk]

Extracted from #20773.

For example, timing out when fuzzing an interpreter is to be expected.

std.testing.fuzzInput should gain an option that allows making timeouts count as a pass.

Right now, timeouts are not implemented; the fuzzer will not detect an endless loop. This issue is to implement timeouts counting as a failure by default, along with an option to make them instead count as a pass.

Timeouts are harmful for fuzzer performance, however, so even a "pass" should indicate to the fuzzer to avoid this input because it will waste time.