has_ts_combined() ->
combined
Check how the terminal handles combined scale and width text sizing
Must be called in raw mode. Sends OSC 66 ; s=2:w=2 ; <space> then
reads the resulting cursor position. A 4-cell advance means the terminal
uses combined semantics (s × w cells); a 2-cell advance means
width-only semantics. Results are cached after the first call.