gh-134209: use heap-allocated memory in `_curses.window.{instr,getstr}` (GH-134283)

* made curses buffer heap allocated instead of stack
* change docs to explicitly mention the max buffer size
* changing GetStr() function to behave similarly too
* Update Doc/library/curses.rst
* Update instr with proper return error handling
* Update Modules/_cursesmodule.c
* change to strlen and better memory safety
* change from const int to Py_ssize_t
* add mem allocation guard
* update versionchanged to mention it was an increase.
* explicitly use versionchanged 3.14 as that is its own branch now.

TESTED: `python -m test -u curses test_curses`

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Co-authored-by: blurb-it[bot] <43283697+blurb-it[bot]@users.noreply.github.com>
Co-authored-by: Gregory P. Smith <greg@krypto.org>
Co-authored-by: Bénédikt Tran <10796600+picnixz@users.noreply.github.com>