Migrate nullability annotations to jSpecify

Mojang has done that, we don't need 3 different sets of annotations

src/main/java/carpet/script/exception/Throwables.java

@@ -1,6 +1,6 @@
 package carpet.script.exception;
 
-import javax.annotation.Nullable;
+import org.jspecify.annotations.Nullable;
 import java.util.HashMap;
 import java.util.Map;