Fix stop cancellation in case of repeated scheduled times

[leonardehrenfried]

Summary

It fixes a strange edge case where repeated times in the schedule lead to an inability to SKIP stops with a GTFS-RT TripUpdate.

Issue

Closes #6848

Unit tests

A module test was added.

Documentation

Javadoc.

cc @laurentg

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.08%. Comparing base (a4136ad) to head (48ff0a4).
⚠️ Report is 94 commits behind head on dev-2.x.

Additional details and impacted files

@@            Coverage Diff             @@
##             dev-2.x    #6849   +/-   ##
==========================================
  Coverage      72.08%   72.08%           
- Complexity     19517    19518    +1     
==========================================
  Files           2105     2105           
  Lines          78976    78977    +1     
  Branches        8007     8007           
==========================================
+ Hits           56930    56931    +1     
+ Misses         19228    19227    -1     
- Partials        2818     2819    +1     

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[miklcct]

Thanks. Can't see any problem with your approach as the scheduled diff is always 0 in this case for the cancelled stops, so the interpolated times are always the same as the previous non-cancelled stop.