Fix axis labeller + free facets

[grantmcdermott]

Fixes #374

Also fixes user-specified x/ylim compatibility with free facets, which I picked up while testing.

Example:

pkgload::load_all("~/Documents/Projects/tinyplot")
#> ℹ Loading tinyplot

plt(mpg ~ wt, mtcars, facet = ~am, facet.args = list(free = TRUE),
    xlim = c(0, 10), xaxl = "$")

^{Created on 2025-05-02 with reprex v2.1.1}