properly support verbatim ipv6 addresses

pkgs/clan-cli/clan_cli/ssh/__init__.py

@@ -845,6 +845,10 @@ def parse_deployment_address(
         meta = {}
     parts = host.split("@")
     user: str | None = None
+    # count the number of : in the hostname
+    if host.count(":") > 1 and not host.startswith("["):
+        msg = f"Invalid hostname: {host}. IPv6 addresses must be enclosed in brackets , e.g. [::1]"
+        raise ClanError(msg)
     if len(parts) > 1:
         user = parts[0]
         hostname = parts[1]