Fix zlib code examples.

[ericonr]

• buffer_out will receive a binary stream, it should be unsigned char
• strlen shouldn't be used on a binary stream; the actual compression result is in z_stream.total_out [1]
• strlen() returns a size_t, so we should use "%zu" format specifier

[1] https://stackoverflow.com/questions/12840933/compressed-file-size-after-deflate

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[memsharded]

Thanks for your contribution.
Supporting code for the docs, as described in those documentation pages is in this repo: https://github.com/conan-io/examples2

The first PR needs to target that repo, and only when it has been merged, update the documentation

[memsharded]

Hi @ericonr

Do you think you could submit the PR to https://github.com/conan-io/examples2/pulls to support this one?

[ericonr]

For sure!
Just haven't had the time for it. Will try to get to it ASAP