New APIs for message processing loops

This patch adds new C APIs
dc_get_next_msgs() and dc_wait_next_msgs(),
and their JSON-RPC counterparts
get_next_msgs() and wait_next_msgs().

New configuration "last_msg_id"
tracks the last message ID processed by the bot.
get_next_msgs() returns message IDs above
the "last_msg_id".
wait_next_msgs() waits for new message notification
and calls get_next_msgs().
wait_next_msgs() can be used to build
a separate message processing loop
independent of the event loop.

Async Python API get_fresh_messages_in_arrival_order()
is deprecated in favor of get_next_messages().

Introduced Python APIs:
- Account.wait_next_incoming_message()
- Message.is_from_self()
- Message.is_from_device()

Introduced Rust APIs:
- Context.set_config_u32()
- Context.get_config_u32()

src/message.rs

@@ -1468,6 +1468,12 @@ pub async fn markseen_msgs(context: &Context, msg_ids: Vec<MsgId>) -> Result<()>
         return Ok(());
     }
 
+    let old_last_msg_id = MsgId::new(context.get_config_u32(Config::LastMsgId).await?);
+    let last_msg_id = msg_ids.iter().fold(&old_last_msg_id, std::cmp::max);
+    context
+        .set_config_u32(Config::LastMsgId, last_msg_id.to_u32())
+        .await?;
+
     let msgs = context
         .sql
         .query_map(