`pch` should accept character literals

[grantmcdermott]

Saw a post by @yjunechoe on social media that reminded me of this:

library(tinyplot)

xx = rnorm(1e4)

plot(xx, pch = ".")

tinyplot(xx, pch = ".")
#> Error: `pch` must be `NULL` or a numeric vector of length 1 or 1.

^{Created on 2025-03-11 with reprex v2.1.1}