refactor: Unify naming of direct/single/1:1/normal chats (#8442)

Unifies internal naming of single/direct/1:1/normal chats
to match the naming used in the API.

Closes: #8368
Signed-off-by: Jagoda Ślązak <jslazak@jslazak.com>

---------

Signed-off-by: Jagoda Ślązak <jslazak@jslazak.com>

src/securejoin.rs

@@ -657,7 +657,7 @@ pub(crate) async fn handle_securejoin_handshake(
                 return Ok(HandshakeMessage::Ignore);
             }
             contact_id.regossip_keys(context).await?;
-            // for setup-contact, make Alice's one-to-one chat with Bob visible
+            // for setup-contact, make Alice's single chat with Bob visible
             // (secure-join-information are shown in the group chat)
             if grpid.is_empty() {
                 ChatId::create_for_contact(context, contact_id).await?;