Dyanmic themes: axis titles not centered with long perpendicular labels

[grantmcdermott]

The "Petal.Width" x-axis title here should be centered between 1.0 and 1.5.

tinyplot::plt(Petal.Width ~ I(paste0("Species: ",Species)), data = iris, theme = 'clean', flip = TRUE, ylim = c(0, 2.5))

^{Created on 2026-04-27 with reprex v2.1.1}

Related to #479.