calendar_precision()
extracts the precision from a calendar object. It
returns the precision as a single string.
Examples
calendar_precision(year_month_day(2019))
#> [1] "year"
calendar_precision(year_month_day(2019, 1, 1))
#> [1] "day"
calendar_precision(year_quarter_day(2019, 3))
#> [1] "quarter"