bpo-38687: Expose zlib 'adler32_combine' function to Python zlib module

[CallumAttryde]

zlib contains a function for combining Adler32 checksums which is not currently exposed by the Python module. This enhancement adds that functionality to Python

https://bugs.python.org/issue38687

[the-knights-who-say-ni]

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[emmatyping]

Closing as this was resolved in #134650