Don't evaluate (title) annotations

[grantmcdermott]

Fixes #624

pkgload::load_all("~/Documents/Projects/tinyplot/")
#> ℹ Loading tinyplot
plt(0, 0, main = bquote(pi == .(pi)))

plt(0, 0, main = bquote(foo == .(pi)))

^{Created on 2026-06-22 with reprex v2.1.1}