Align zlib behavior with CRuby

[headius]

Our zlib library was very roughly ported from CRuby many years ago, as described in #4835 (comment). Unfortunately this logic has not kept up with changes and improvements in CRuby, leading to issues like #6606.

We should try to align our logic with CRuby and get all available tests passing, to avoid future incompatibility reports.

The original folks that worked on this may be interested in helping: @nahi @ymnk.

[headius]

This has not happened, but there's a big pile of zlib-related issues in the tracker that an update would fix (if they are not fixed already:

• Zlib::GzipReader#level never get updated #1840
• Zlib deflate now takes a block for streaming results #2128
• Zlib::Deflate #deflate memory leak #3962
• Zlib produces different output to MRI #4244
• Zlib::GzipWriter.wrap - MRI doesn't close IO object when finish is called, but JRuby does #4249
• Zlib::Inflate - Getting Zlib::BufError inflating a string #4449
• Zlib.inflect raises a Zlib::BufError instead of a Zlib::DataError #7482
• New failures in Rack tests relating to deflater #7879

And possibly others that are peripherally caused by zlib incompatibilities.

We recently forked jzlib to fix #1422 (recently uncovered by the rack team) so it should be possible to fix these other cases now.

Bumping to 9.4.5.0 but I'll probably be the one looking into it.