gh-152275: Add integer overflow guards to the curses chtype and color-pair packing...

gh-152275: Add integer overflow guards to the curses chtype and color-pair packing path (GH-152303)

curses.color_pair() now raises OverflowError for a pair number too large
to be packed, instead of silently masking it to a different pair.

The attr argument of the character-cell and attribute methods (addch,
addstr, attron, attrset and others) now goes through the checked attr
converter, so an out-of-range or non-integer attribute is rejected rather
than silently truncated.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>