As noted in #40604, we're seeing cases where we need to wait
`onboardingAutoCloseAge+1` days until the onboarding PR will be
auto-closed.
To fix this, we can refactor `getElapsedDays` to optionally return a
floating point number, which we can then perform more careful
calculations against.
As we're now being a little more careful with timings being used for our
date comparisons, we need to make sure that Vitest fakes our timer
during these tests.
Instead of long floating-point numbers, we should use a 2 decimal
place value for log messages, as they're more readable to humans.
Sergei Zharinov