StubTestHookTimeNow stubs all `Now()` use for ydb packages.
It sets up current time to given now time.
It returns time shifter function that shifts current time by given
duration.
It returns cleanup function that MUST be called after test execution.
NOTE: tests using this function MUST not be called concurrently.
AfterFunc waits for the duration to elapse and then calls f
in its own goroutine. It returns a Timer that can
be used to cancel the call using its Stop method.