…rray methods

Add the immutable curses.complexstr type, an array of styled wide-character
cells -- the string counterpart of complexchar.  It is constructible from an
iterable of cells (each a complexchar or a str) or from a string split into
cells, with optional attr and pair applied to every cell.  It is an immutable
sequence (indexing yields a complexchar, slicing and concatenation yield a
complexstr), is hashable, and str() returns its cells' text.

Add the window method in_wchstr(), the wide-character counterpart of instr()
and in_wstr() that keeps each cell's attributes and color pair instead of
stripping them; it returns a complexstr.

The methods addstr(), addnstr(), insstr() and insnstr() now also accept a
complexstr, so a run read with in_wchstr() can be written back unchanged.  The
cells carry their own rendition, so combining one with an explicit attr raises
TypeError.

This is the second step of the cchar_t API (cell arrays), after the single-cell
complexchar type.

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