Function get_table_columns 

pub async fn get_table_columns(
    client: &Client,
    schema: &str,
    table: &str,
) -> Result<Vec<(String, String)>>

Extract column metadata from a PostgreSQL table.

Returns (column_name, data_type) pairs for all columns in the table. Uses udt_name from information_schema which includes array type info (e.g., _text for text[], _int4 for integer[]).