Platoons social functionality (#91)

### Description

This implements and completes #87 (to the best of my knowledge)

### Game

Robocraft

### Please confirm

- [x] I am the legal owner or represent the owner of all work submitted
- [x] I consent to my submission being added to this FOSS project
- [ ] This PR used LLMs to generate some or all of the code changes

Reviewed-on: https://git.ngram.ca/OpenJam/rc-servers/pulls/91
Co-authored-by: NG (Graham) <ngniusness@gmail.com>
Co-committed-by: NG (Graham) <ngniusness@gmail.com>

rc_social_room/src/operations/platoon_leave.rs

@@ -0,0 +1,65 @@
+use polariton_server::operations::{SimpleOpError, SimpleOperation, SimpleOpImpl};
+use polariton::operation::ParameterTable;
+
+const CODE: u8 = 13;
+
+pub(super) struct PlatoonLeaver {
+    social: std::sync::Arc<crate::SocialMesh>,
+}
+
+#[async_trait::async_trait]
+impl SimpleOperation<crate::data::custom::CustomType> for PlatoonLeaver {
+    type User = crate::UserTy;
+    const CODE: u8 = CODE;
+
+    async fn handle(&self, params: ParameterTable<crate::data::custom::CustomType>, user: &Self::User) -> Result<ParameterTable<crate::data::custom::CustomType>, SimpleOpError> {
+        let user_info = user.user()?;
+        let my_public_id = user_info.public_id();
+        if let Some(platoon_id) = self.social.platoon_of_user(my_public_id).await {
+            log::debug!("User {} left platoon {}", my_public_id, platoon_id);
+            let members = self.social.users_of_platoon(&platoon_id).await;
+            if members.len() <= 2 {
+                self.social.remove_platoon(&platoon_id).await;
+                let event = crate::events::platoon_removed::PlatoonDisbanded {
+                    platoon_id: platoon_id.to_owned(),
+                };
+                for member in members.iter() {
+                    if member.public_id == my_public_id { continue; }
+                    self.social.send_event_to(&member.public_id, event.clone()).await;
+                }
+                log::debug!("Platoon {} removed", platoon_id);
+            } else {
+                self.social.remove_user_from_platoon(my_public_id).await;
+                let event = crate::events::platoon_member_left::PlatoonMemberLeft {
+                    member_public_id: my_public_id.to_owned(),
+                    member_display_name: user_info.display_name().to_owned(),
+                };
+                for member in members.iter() {
+                    if member.public_id == my_public_id { continue; }
+                    self.social.send_event_to(&member.public_id, event.clone()).await;
+                }
+                if members[0].public_id == my_public_id {
+                    // current user was the leader; there is now a new leader
+                    log::debug!("User {} is now the leader of platoon {}", members[1].public_id, platoon_id);
+                    let social_info = user_info.list_social_info(&[members[1].public_id.clone()]).await?;
+                    let event = crate::events::platoon_leader_changed::PlatoonLeaderChanged {
+                        leader_public_id: social_info[0].public_id.clone(),
+                        leader_display_name: social_info[0].display_name.clone(),
+                    };
+                    for member in members.iter() {
+                        if member.public_id == my_public_id { continue; }
+                        self.social.send_event_to(&member.public_id, event.clone()).await;
+                    }
+                }
+            }
+
+        }
+        Ok(params)
+    }
+}
+
+pub(super) fn platoon_leave_provider(init_ctx: &crate::InitConfig) -> SimpleOpImpl<crate::data::custom::CustomType, crate::UserTy, PlatoonLeaver> {
+    SimpleOpImpl::new(PlatoonLeaver {
+        social: init_ctx.social.clone(),
+    })
+}