gh-152470: Make wide-character curses functions work on a narrow build (GH-152476)

gh-152470: Make wide-character curses functions work on a narrow build (GH-152476)

curses.window.get_wch, curses.window.get_wstr, curses.unget_wch,
curses.erasewchar, curses.killwchar and curses.wunctrl now also work when
Python is built against a non-wide curses library, on an 8-bit locale, where
each character is a single byte in the relevant encoding.  curses.ungetch now
also accepts a one-character string, like curses.unget_wch.

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>