Enhance documentation by adding argument descriptions to functions in historic_vol, pivots, reduce_df, and update_df modules

src/utils/qdf/reduce_df.rs

@@ -7,6 +7,7 @@ use std::error::Error;
 const QDF_INDEX_COLUMNS: [&str; 3] = ["real_date", "cid", "xcat"];
 
 /// Filter a dataframe based on the given parameters.
+/// # Arguments:
 /// - `cids`: Filter by cross-sectional identifiers
 /// - `xcats`: Filter by extended categories
 /// - `metrics`: Filter by metrics