feat: Add ClientJoinWorldCallback event

This event gets fired whenever the client joins a new world (can be
internal, or external). This will soon be used for a new feature which
will allow you to clear the message counters when you join a new world.

src/main/java/dev/cbyrne/compactchat/event/ClientJoinWorldCallback.java

@@ -0,0 +1,20 @@
+package dev.cbyrne.compactchat.event;
+
+import net.fabricmc.fabric.api.event.Event;
+import net.fabricmc.fabric.api.event.EventFactory;
+
+/**
+ * Fired whenever the client 'joins' a new world. This can be either an internal (single-player) or external (multiplayer) world.
+ * @see net.minecraft.client.MinecraftClient#joinWorld(net.minecraft.client.world.ClientWorld)
+ */
+public interface ClientJoinWorldCallback {
+    Event<ClientJoinWorldCallback> EVENT = EventFactory.createArrayBacked(ClientJoinWorldCallback.class,
+        (listeners -> () -> {
+            for (var listener : listeners) {
+                listener.onJoin();
+            }
+        })
+    );
+
+    void onJoin();
+}

src/main/java/dev/cbyrne/compactchat/mixin/MinecraftClientMixin.java

@@ -0,0 +1,16 @@
+package dev.cbyrne.compactchat.mixin;
+
+import dev.cbyrne.compactchat.event.ClientJoinWorldCallback;
+import net.minecraft.client.MinecraftClient;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+@Mixin(MinecraftClient.class)
+public class MinecraftClientMixin {
+    @Inject(at = @At("HEAD"), method = "joinWorld")
+    private void compactChat$joinWorldHandler(CallbackInfo ci) {
+        ClientJoinWorldCallback.EVENT.invoker().onJoin();
+    }
+}

src/main/resources/CompactChat.mixins.json

@@ -7,7 +7,8 @@
   ],
   "client": [
     "ChatHudMixin",
-    "KeyboardMixin"
+    "KeyboardMixin",
+    "MinecraftClientMixin"
   ],
   "injectors": {
     "defaultRequire": 1