v3.15.0b4
[3.15] gh-150285: Fix too long docstrings in the zstd module (GH-150291) (GH-150335)
gh-128341: Use _Py_ABI_SLOT in stdlib modules (#145770)
GH-136975: Emend a spelling error (algorthm -> algorithm) (#136999)
gh-139877: Use PyBytesWriter in pycore_blocks_output_buffer.h (#139976)
[3.15] gh-150583: Fix zstd compression level with digested ZstdDict (GH-150586) (#153883)
[3.15] gh-148286: Fix UB in `ZstdDecompressor.unused_data` when a frame is decompressed in one call (GH-153258) (#153644)