Determine most recent highlighted annotation by its updated date

[acelaya]

Following up on #6338, do an actual check of highlighted annotations dates to determine which one is the most recent one, instead of implicitly trusting their order in the store.

This logic is more robust and future-proof, in case the logic to add them to the store eventually changes.

Testing

You can follow the same steps described in #6338

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.43%. Comparing base (239a63b) to head (75a1a05).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6341   +/-   ##
=======================================
  Coverage   99.43%   99.43%           
=======================================
  Files         271      271           
  Lines       10224    10231    +7     
  Branches     2420     2424    +4     
=======================================
+ Hits        10166    10173    +7     
  Misses         58       58           

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[robertknight]

LGTM