Function columns_taxonomy 

fn columns_taxonomy(
    batch_schema: &Arc<Schema>,
    table_name: &str,
    name_to_ids: &HashMap<String, u32>,
    partition_columns: &HashSet<&str>,
) -> Result<(Vec<TagColumnInfo>, SmallVec<[usize; 3]>)>

Classifies columns in a logical-table batch for sparse primary-key conversion.

Returns:

• Vec<TagColumnInfo>: all Utf8 tag columns sorted by tag name, used for TSID and sparse primary-key encoding.
• SmallVec<[usize; 3]>: indices of columns copied into the physical batch after __primary_key, ordered as [greptime_timestamp, greptime_value, partition_tag_columns...].