v3.15.0b4
[3.15] gh-143008: Fix race re-initializing TextIOWrapper (#151203)
[3.15] gh-150285: Fix too long docstrings in the io module (GH-150287) (GH-150332)
gh-141376: Fix exported symbols (GH-141377)
[3.15] gh-149816: add missing critical section on self in buffered_iternext (GH-150295) (#150305)
[3.15] gh-151640: Track sharing of `BytesIO` buffer in free-threaded builds (GH-151651) (gh-153151)
[3.15] gh-149046: fix: correctly handle `str` subclasses in `io.StringIO` (GH-149047) (#150706)
[3.15] gh-151814: Fix unbounded memory growth from repeated empty writes to `io.TextIOWrapper` (GH-151817)