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/config.rs

@@ -308,6 +308,9 @@ pub enum Config {
     /// This value is used internally to remember the MsgId of the logging xdc
     #[strum(props(default = "0"))]
     DebugLogging,
+
+    /// Last message processed by the bot.
+    LastMsgId,
 }
 
 impl Context {
@@ -358,6 +361,11 @@ impl Context {
         Ok(self.get_config_parsed(key).await?.unwrap_or_default())
     }
 
+    /// Returns 32-bit unsigned integer configuration value for the given key.
+    pub async fn get_config_u32(&self, key: Config) -> Result<u32> {
+        Ok(self.get_config_parsed(key).await?.unwrap_or_default())
+    }
+
     /// Returns 64-bit signed integer configuration value for the given key.
     pub async fn get_config_i64(&self, key: Config) -> Result<i64> {
         Ok(self.get_config_parsed(key).await?.unwrap_or_default())
@@ -459,6 +467,12 @@ impl Context {
         Ok(())
     }
 
+    /// Set the given config to an unsigned 32-bit integer value.
+    pub async fn set_config_u32(&self, key: Config, value: u32) -> Result<()> {
+        self.set_config(key, Some(&value.to_string())).await?;
+        Ok(())
+    }
+
     /// Set the given config to a boolean value.
     pub async fn set_config_bool(&self, key: Config, value: bool) -> Result<()> {
         self.set_config(key, if value { Some("1") } else { Some("0") })