Use explicit integers in `year()` and `month()`

[malcolmbarrett]

An astute student pointed out to use that day(), year() and month() are inconsistent in their return types:

library(lubridate)
x <- ymd("2012-03-26")
is.integer(month(x))
#> [1] FALSE
is.integer(day(x))
#> [1] TRUE
is.integer(year(x))
#> [1] FALSE

^{Created on 2022-12-15 with reprex v2.0.2}

This seems like an unintentional conversion due to addition. This PR uses explicit integer addition to have month() and year() return integers

[vspinu]

This has been attempted before The consequences are not as benign as they might appear.

Let's try to give it another try, but not for the forthcoming release (end of this month) but for the next one. leaving this open till then.

[malcolmbarrett]

Sounds good. Happy to help with revdep fallout when the time comes. Just let me know