MailCraft crates/jmap's protocol core at a44a450, moved as it is with all
its tests: session, requests with result references, responses, ids,
addresses and templates, credentials, retry and the judgement of HTTP
answers, over any HttpExchange. The mail client on top stays in MailCraft.
Co-authored-by: Martin Ball <98639962+benandez@users.noreply.github.com>