Formatting a naive-time with `%Z` or `%z` should result in a warning or error

[DavisVaughan]

All results will be NA, so maybe an error?

library(clock)
x <- as_naive_time(year_month_day(2019, 1, 1))
format(x, format = "%Z")
#> [1] NA

^{Created on 2021-04-06 by the reprex package (v1.0.0)}