Port to 1.21 & Improve Performance

- Only the required textures are now loaded on startup -> Faster startup, less RAM usage
- Removed Boss Bar loading bar design, as it became a huge maintenance burden
- Added unifiedPublishing to streamline update deployment

settings.gradle

@@ -5,6 +5,7 @@ pluginManagement {
             name = 'Fabric'
             url = 'https://maven.fabricmc.net/'
         }
+        maven { url "https://maven.architectury.dev/" }
         gradlePluginPortal()
     }
 }