[BUG] add_partial_keys() Doesn't fully capture arm regex

[rsh52]

Issue Description

The add_partial_keys() function is used to split events and arm names that REDCap provides as a single unique event name, ex: repeat_event_arm_1. add_partial_keys() will split this up into repeat_event and 1.

An oversight we made is when REDCap events are very similarly named:

REDCap can also add additional specifiers that aren't just the numeric value. This means we need to capture that, and convert the arm column from an integer type to a factor type (so in the above example we capture 1b as an arm value.

This will be corrected in the upcoming #205

How to Reproduce the Bug:

The issue occurs here, due to limited regex definition: https://github.com/CHOP-CGTInformatics/REDCapTidieR/blob/82a49b713afff929c6d5df7230acab3085186b21/R/utils.R#L18-L34

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