#61979 [13.x] Fix sub-second process timeouts given as a CarbonInterval

When a timeout shorter than one second is given as a CarbonInterval, the process runs with no timeout at all.

Process::timeout(CarbonInterval::milliseconds(500))->run('redis-cli ping');

This is expected to give up after half a second. Instead the interval is truncated to 0, which means "no timeout", so the command can hang forever.

Fractions are also dropped for longer intervals, so CarbonInterval::milliseconds(1900) becomes a 1 second timeout.