ct_set_defaults() overrides ggplot2 aesthetic defaults via
ggplot2::update_geom_defaults(). v0.1 sets a single override:
geom_point size = 2.5. ct_unset_defaults() restores whatever
values were active the first time ct_set_defaults() ran — not
ggplot2's untouched baseline.
Originals are captured once into a package-private environment, so
repeated ct_set_defaults() calls are idempotent. Column width and
linewidth are handled elsewhere — see ct_col() / ct_line() for
explicit formal overrides, or apply ct_theme() / theme_strategy()
for linewidth via from_theme().