[12.x] chore: remove support for Carbon v2

[calebdw]

Hello!

This removes support for Carbon v2 and cleans up the addReal* methods to use the add* equivalents.

Thanks!

[crynobone]

addReal* was deprecated in Carbon 3.2 but should still work: briannesbitt/Carbon@a6e64c7

It might be best to target master branch for v12 and remove support for Carbon 2

@kylekatarnls does it make more sense to change to addUtcMinutes() instead of addMinutes()?

[calebdw]

Ah, PHPStan was complaining about the methods not existing and I missed the dynamic addRealUnit method

[kylekatarnls]

Hello, use addMinutes(), the UTC prefix would make a difference only for day units and above and only if there is a daylight saving time in the range.

In older versions of PHP there were some bug also during DST when adding hours/minutes, but nowadays, it's behaving in a consistent manner.

[crynobone]

Thanks @kylekatarnls