[11.x] Ensure datetime cache durations account for script execution time

[timacdonald]

This PR addresses a rounding bug when datetime or intervals are used with the cache.

Cache::put($key, $value, now()->addSecond());

Surprisingly, this will not put the value into the cache. It will instead call Cache::forget under the hood.

This is because by the time we do a diff between now() and $ttl = now()->addSecond() some time has passed during PHP execution, even if only microseconds. That means the diff is ~0.999 seconds, which we cast to an int resulting in 0.

This also impacts date time intervals, because we convert those to datetime instances.

I have a gut feeling this also impacts other parts of the framework where we pull the seconds off a datetime, such as the queue system. Also anything that uses InteractsWithTime may also be impacted. Some of those values are likely off by a second. I haven't investigated this to confirm, though.

[timacdonald]

I've changed this from diffInSeconds to diffInMilliseconds / 1000 because Carbon 2 would always return an int while carbon 3 returns a float.

This allows us to ensure we get the correct value on both versions.