Return dataframes with regular column order

Current caching of columns as they are requested jumbles the order of the columns stored in the base dataframe. When calling `Result.data` the columns should be returned in alphabetical order so the same column order is returned every time.

Find the Result.data entry point and inspect how requested columns are cached and assembled into the base dataframe. Verify the current behavior with a focused reproduction, then confirm that repeated calls to Result.data return columns in alphabetical order every time.

Written by the indexing model from the issue text.