OxiPNG support

[astei]

Although modern alternatives to PNG like WebP and AVIF exist today, it is still valuable to ensure we get the most out of older clients which lack WebP or AVIF support. OxiPNG is a rewrite of the venerable OptiPNG in Rust, and amongst it features includes native support for libdeflate and Zopfli which can drastically improve the compression ratio over OptiPNG's highest level of compression.