add ping/pong between client and server

the purpose of this is to hopefully prevent nginx from reaping the connection, since there's data flowing through it every so often

crates/rkgk/src/api/wall.rs

@@ -300,6 +300,10 @@ impl SessionLoop {
 
     async fn process_request(&mut self, ws: &mut WebSocket, request: Request) -> eyre::Result<()> {
         match request {
+            Request::Ping => {
+                ws.send(to_message(&Notify::Pong)).await?;
+            }
+
             Request::Wall { wall_event } => {
                 match &wall_event {
                     // This match only concerns itself with drawing-related events to offload

crates/rkgk/src/api/wall/schema.rs

@@ -69,6 +69,8 @@ pub enum LoginResponse {
     rename_all_fields = "camelCase"
 )]
 pub enum Request {
+    Ping,
+
     Wall {
         wall_event: wall::EventKind,
     },
@@ -95,6 +97,8 @@ pub struct ChunkInfo {
     rename_all_fields = "camelCase"
 )]
 pub enum Notify {
+    Pong,
+
     Wall {
         wall_event: wall::Event,
     },