Stop the FileWatcher when unloading configs.

The FileWatcher needs to be stopped somewhere otherwise the jvm will hang on exit because it is keeping a ScheduledExecutorService thread pool alive with non-daemon threads. Since ConfigTracker.unloadConfigs is called during server stop, it seems like an ok place to also stop the FileWatcher.

loader/src/main/java/net/neoforged/fml/config/ConfigTracker.java

@@ -127,6 +127,9 @@ public void loadConfigs(ModConfig.Type type, Path configBasePath, @Nullable Path
     public void unloadConfigs(ModConfig.Type type) {
         LOGGER.debug(CONFIG, "Unloading configs type {}", type);
         this.configSets.get(type).forEach(ConfigTracker::closeConfig);
+        if (!FMLConfig.getBoolConfigValue(FMLConfig.ConfigValue.DISABLE_CONFIG_WATCHER)) {
+            FileWatcher.defaultInstance().stop();
+        }
     }
 
     static void openConfig(ModConfig config, Path configBasePath, @Nullable Path configOverrideBasePath) {