osu: implement beatmapset and simulate button (#55)

* Prepare a message beforehand for display_beatmapset

* Implement a Beatmapset button

* Always sort top plays by pp

* Show leaderboard for top pp per user/mod only

* Add score simulation

* Store all reaction to be removed later

* Properly handle errors

* Parse beatmap to get placeholders for modal

* Make buttons same color

youmubot-prelude/src/pagination.rs

@@ -27,6 +27,9 @@ pub trait Paginate: Send + Sized {
         Ok(())
     }
 
+    /// Cleans up after the pagination has timed out.
+    async fn cleanup(&mut self, _ctx: &Context, _m: &mut Message) -> () {}
+
     /// Handle the incoming reaction. Defaults to calling `handle_pagination_reaction`, but you can do some additional handling
     /// before handing the functionality over.
     ///
@@ -116,6 +119,10 @@ impl<Inner: Paginate> Paginate for WithPageCount<Inner> {
     fn is_empty(&self) -> Option<bool> {
         Some(self.page_count == 0)
     }
+
+    async fn cleanup(&mut self, ctx: &Context, msg: &mut Message) {
+        self.inner.cleanup(ctx, msg).await;
+    }
 }
 
 #[async_trait::async_trait]
@@ -240,6 +247,8 @@ pub async fn paginate_with_first_message(
         }
     };
 
+    pager.cleanup(ctx, &mut message).await;
+
     for reaction in reactions {
         if reaction.delete_all(&ctx).await.pls_ok().is_none() {
             // probably no permission to delete all reactions, fall back to delete my own.