gh-152219: Add curses window attribute get/set methods and WA_* constants (GH-152221)

gh-152219: Add curses window attribute get/set methods and WA_* constants (GH-152221)

Add the window methods attr_get(), attr_set(), attr_on(), attr_off() and
color_set(), wrapping wattr_get(), wattr_set(), wattr_on(), wattr_off() and
wcolor_set().  Unlike the legacy attron()/attroff()/attrset() methods, these
pass the color pair as a separate argument instead of packing it into the
attribute value.  Also add the corresponding WA_* attribute constants.

Add an attr_converter that range-checks the attr_t attribute argument and
raises OverflowError instead of silently truncating it; apply it to attr_set(),
attr_on(), attr_off() and chgat().

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