Adding flag (f/b) to predictive column name

[Jday7879]

Summary

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Minor bug fixes in flag_matched_pair_merge and flag_matched_pair_shift

Checklists

This pull request meets the following requirements:

• installable with all dependencies recorded
• runs without error
• follows PEP8 and project specific conventions
• appropriate use of comments, for example no descriptive comments
• functions documented using Numpy style docstings
• assumptions and decisions log considered and updated if appropriate
• unit tests have been updated to cover essential functionality for a reasonable range of inputs and conditions
• other forms of testing such as end-to-end and user-interface testing have been considered and updated as required
• tests suite passes (locally as a minimum)
• peer reviewed with review recorded

If you feel some of these conditions do not apply for this pull request, please
add a comment to explain why.

[AntonZogk]

@Jday7879 all looking great, nothing to add