zero_range() casts to numeric

[teunbrand]

This PR aims to fix #468 and by extension fix tidyverse/ggplot2#6134.

Briefly, we cast input x to numeric before doing computations for the range.

devtools::load_all("~/packages/scales//")
#> ℹ Loading scales

range <- structure(c(1234, 7380), class = "difftime", units = "secs")

zero_range(range)
#> [1] FALSE

ggplot2::resolution(range, zero = FALSE)
#> [1] 6146

^{Created on 2024-10-11 with reprex v2.1.1}

[teunbrand]

Also if just 1 of the 2 numbers are infinite we have non-zero range. (same-sign infinites are handled above)