Migrate nullability annotations to jSpecify

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

src/main/java/carpet/script/value/ValueConversions.java

@@ -60,7 +60,7 @@ import java.util.UUID;
 import java.util.function.Predicate;
 import java.util.stream.StreamSupport;
 
-import javax.annotation.Nullable;
+import org.jspecify.annotations.Nullable;
 
 public class ValueConversions
 {