Refactor: Separate the Siri TripUpdate into AddedTrip and ModifiedTrip classes

[habrahamsson-skanetrafiken]

Summary

This is a pure refactor that separates the siri TripUpdate object into two different records depending on whether the trip is being modified or if a new trip is being added.

The nice thing about having two separate records for SiriAddTrip and SiriModifyTrip is that it's clearer what properties are actually valid depending on the use case, instead of having a big record with lots of nullable fields that is difficult to understand when you can expect different fields to be present or not.

Unit tests

There is pretty good test coverage from before of this piece of code.

Bumping the serialization version id

No.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.10%. Comparing base (b9ebbd3) to head (02db3e7).
Report is 4 commits behind head on dev-2.x.

Additional details and impacted files

@@            Coverage Diff             @@
##             dev-2.x    #6489   +/-   ##
==========================================
  Coverage      70.10%   70.10%           
+ Complexity     18269    18263    -6     
==========================================
  Files           2077     2077           
  Lines          77658    77658           
  Branches        7827     7827           
==========================================
+ Hits           54439    54440    +1     
+ Misses         20441    20440    -1     
  Partials        2778     2778           

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[habrahamsson-skanetrafiken]

Converting to draft for now, let's merge vincents Extra call pr before this