jid: Validate domains against idna

The idna crate validates against UTS 46, which supports domains using
either IDNA2003 or IDNA2008.  This allows us to support both old and
new internationalized domain names.

This dependency isn’t a new one in the tree, as hickory-proto, url and
tokio-xmpp all were already depending on it.

There are a bunch of other checks that have to be performed, this is
inspired by slixmpp’s JID implementation.

jid/CHANGELOG.md

@@ -3,6 +3,8 @@ Version NEXT:
     - Add missing check for JIDs with too many `@` before the resource, such as
       `a@b@c` or `a@b@c/d` which should clearly be invalid.  The new error it
       produces is named `TooManyAts`.
+    - domainparts are now checked much more in-depth, using the idna crate and
+      various custom rules.
 
 Version 0.11.1, release 2024-07-23:
   * Breaking: