Fix memory leak in TimetableSnapshot related to patternsForStop

[VillePihlava]

Summary

For some reason patternsForStop is not cleared in the clear method of TimetableSnapshot. This seems to cause a memory leak. This PR adds a clear function to do this. We are currently testing this to see if it fixes our release-blocking performance problems. Even if it doesn't fix them, I think this should still be merged.

Issue

N/A

Unit tests

N/A

Documentation

Added javadoc and improved existing ones

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 72.14%. Comparing base (fb577ad) to head (8a329df).
⚠️ Report is 16 commits behind head on dev-2.x.

Additional details and impacted files

@@              Coverage Diff              @@
##             dev-2.x    #7253      +/-   ##
=============================================
+ Coverage      72.12%   72.14%   +0.02%     
- Complexity     21085    21089       +4     
=============================================
  Files           2297     2297              
  Lines          85223    85235      +12     
  Branches        8487     8489       +2     
=============================================
+ Hits           61465    61492      +27     
+ Misses         20781    20767      -14     
+ Partials        2977     2976       -1     

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[optionsome]

@tkalvas should realTimeAddedReplacedByTripOnServiceDateById be cleared as well?

[tkalvas]

@tkalvas should realTimeAddedReplacedByTripOnServiceDateById be cleared as well?

Yes, definitely. Although this only comes into play if updateIncrementality == FULL_DATASET, but then it is a clear mistake that I didn't include it.

[optionsome]

I think TimetableSnapshot#isEmpty should probably check that all of these collections are empty and we could improve tests for it so that the snapshot is empty after it's cleared.