gh-155742: Use PyBytesWriter in zlib

[vstinner]

Replace soft deprecated _PyBytes_Resize() with PyBytesWriter.

• Issue: Treat bytes objects as immutable in C code #155742

[vstinner]

I marked the PR as a draft since benchmarks should be run on this change.

_PyBytes_Resize(n) allocates exactly n bytes, whereas PyBytesWriter_Resize(n) overallocates the buffer.

See also PR gh-139976 which modified _bz2, _lzma, _zstd and zlib extensions to use PyBytesWriter (in pycore_blocks_output_buffer.h).