Function duckdb_appender_clear_columns 

pub unsafe extern "C" fn duckdb_appender_clear_columns(
    appender: duckdb_appender,
) -> duckdb_state

Removes all columns from the active column list of the appender, resetting the appender to treat all columns as active. Immediately flushes all previous data.

@param appender The appender to clear the columns from. @return DuckDBSuccess on success or DuckDBError on failure.