[feature request] Support for Zstandard Content-Encoding

[grr]

If IO::Uncompress::UnZstd is installed, support Zstandard content encoding (zstd).

References:

• https://blog.cloudflare.com/new-standards/
• https://caniuse.com/zstd

[mikkoi]

HTTP-Message could contain a util method to handle Accept-Encoding header.

Should the actual decision be in UserAgent?

[grr]

LWP::UserAgent docs points to where it is handled:
https://metacpan.org/pod/LWP::UserAgent#default_header
https://metacpan.org/dist/HTTP-Message/source/lib/HTTP/Message.pm#L487

But that's only handling the header. You still need to add support for encoding and decoding in encode and decoded_content, respectively.

[mikkoi]

Would we always have Accept-Encoding: zstd in http request if we have the library?

[grr]

As the doc for LWP::UserAgent shows (linked in my previous reply), the user has to specify any Accept-Encoding header.