[3.14] gh-159617: Fix _pyrepl dropping the end of long wrapped lines

[lazerg]

In 3.14, Reader.calc_screen() sizes the wrap loop as (width_of_line + prompt) // console_width rows, but each wrapped row only holds console_width - 1 characters because of the \ marker. On long lines the loop ends early, so the tail of the line never reaches screeninfo, and moving down to those rows raises IndexError in max_column(). For example, 19 characters at width 10 already lose the last one.

The loop now runs until the whole line is placed. main and 3.15 don't have this bug, since gh-148105 rewrote the layout code there, so this PR targets 3.14 only. 3.13 has the same loop, so it could take this fix as well.

• Issue: _pyrepl: IndexError in max_column when recalling a very long single-line history entry #159617