Change K.1.1 part 3 lookback interval for 2 year visit to 18 months

[mrnosal]

The logic for Section K.1 (patients under 25 after abnormal screening result) heading 3 has been updated to look for most recent low grade cytology results 18 months to 3 years after initial low grade cytology result. Previously it was 2 years to 3 years. Note that K.1 5a and 5b have not changed their look-back interval (still >= 2 years and <=3 years), so there is additional code to handle both intervals. If the look-back for these two is updated to 18mo, then we can simplify the code. This fixes ccsmcds-45

[mrnosal]

GM agrees that K.1 5a and 5b should also be changed to >= 18mo and <=3 years to match K.1 heading 3

[mickohanlon23]

I approved since this code is correct and contributes to CCSMCDS-72, but a new pull request should be opened to address CCSMCDS-45.

As for this branch, we can either merge as-is, or add the rest of the surveillance interval updates to this branch. Either way, I would propose changing the name and description of this pull request and of the ultimate squash commit name to avoid confusion.