feat(annotations): add command containers (#364)

This is the first part of the introduction of annotation processing to cloud. A new `@CommandContainer` annotation has been introduced, which can be placed on classes to have the annotation parser automatically construct & parse the classes when `AnnotationParser.parseContainers()` is invoked.

A future PR will introduce another processor that will scan for `@CommandMethod` annotations and verify the integrity of the annotated methods (visibility, argument annotations, etc.).

examples/example-bukkit/build.gradle.kts

@@ -18,6 +18,8 @@ dependencies {
     implementation(libs.adventurePlatformBukkit)
     /* Bukkit */
     compileOnly(libs.bukkit)
+    /* Annotation processing */
+    annotationProcessor(project(":cloud-annotations"))
 }
 
 tasks {