create table t(x int) with ('skip_unused_columns' = 'true');

generates

        catalog.register_input_zset::<_, struct_9acc8893116a5dd9>(s0.clone(), handle_s0.clone(), r#"{"name":"t","case_sensitive":false,"fields":[{"name":"x","case_sensitive":false,"columntype":{"nullable":true,"type":"INTEGER"},"unused":false}],"materialized":false,"foreign_keys":[]}"#);

Note that the table schema is missing the properties field, including skip_unused_columns. The reason for making skip_unused_columns a table attribute was to make sure that changing the attribute value will trigger backfill. In addition, this attribute is used by the delta connector. I think it needs to be part of the schema, but probably without line numbers..