Misc facet fixes

[grantmcdermott]

Fixes #582
Fixes #583
Fixes #584
Fixes #585

Leads to a lot of regenerated snapshots, but most of these are very minor changes (improvements).

MWE

One example to demo all four fixes:

pkgload::load_all("~/Documents/Projects/tinyplot/")
#> ℹ Loading tinyplot
mtcars$am2 = paste0("AM: ", mtcars$am, "\nCYL: ", mtcars$cyl)
tinyplot(
  mpg ~ wt, facet = ~am2, data = mtcars,
  facet.args = list(cex = 1.3),
  theme = "clean"
)
box('inner')

^{Created on 2026-05-15 with reprex v2.1.1}