Upgrade or remove vendored zlib?

[lalten]

The vendored zlib which is used in zsync2 is based on zlib v1.2.1.1, which is now more than 20 years old.
Any considerations to either get rid of it or to upgrade to a more recent version?

Here's a patch file I generated by diffing the original zsync's sources with the zlib release they're based on: https://github.com/lalten/zsync/blob/76ba13e254d93d9949feffe3e4171fc49e5be488/c/zlib/zlib_1211.patch

And here is the same patch rebased to the latest zlib, 1.3.1
https://github.com/lalten/zsync/blob/76ba13e254d93d9949feffe3e4171fc49e5be488/c/zlib/zlib_131.patch

[probonopd]

@TheAssassin wdyt?