Static start time and clear events

[jeddai]

• Adds methods in Kotlin/Swift to clear the event store
• Adds Swift methods to wait for operation queues to finish
• Updates event store to default its starting time to the beginning of the year

https://mozilla-hub.atlassian.net/browse/EXP-2965
https://mozilla-hub.atlassian.net/browse/EXP-2957

Pull Request checklist

• Quality: This PR builds and tests run cleanly
  • Note:
    • For changes that need extra cross-platform testing, consider adding [ci full] to the PR title.
    • If this pull request includes a breaking change, consider cutting a new release after merging.
• Tests: This PR includes thorough tests or an explanation of why it does not
• Changelog: This PR includes a changelog entry in CHANGES_UNRELEASED.md or an explanation of why it does not need one
  • Any breaking changes to Swift or Kotlin binding APIs are noted explicitly
• Dependencies: This PR follows our dependency management guidelines
  • Any new dependencies are accompanied by a summary of the due dilligence applied in selecting them.

Branch builds: add [ff-android: firefox-android-branch-name] and/or [fenix: fenix-branch-name] to the PR title.

[codecov-commenter]

Codecov Report

Base: 46.15% // Head: 46.27% // Increases project coverage by +0.12% 🎉

Coverage data is based on head (710bf4e) compared to base (4525f96).
Patch coverage: 86.48% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5279      +/-   ##
==========================================
+ Coverage   46.15%   46.27%   +0.12%     
==========================================
  Files         178      178              
  Lines       14274    14320      +46     
==========================================
+ Hits         6588     6627      +39     
- Misses       7686     7693       +7     

Impacted Files	Coverage Δ
components/nimbus/src/lib.rs	68.45% <0.00%> (-0.78%)	⬇️
components/nimbus/src/behavior.rs	87.72% <61.53%> (-0.43%)	⬇️
components/nimbus/src/tests/test_behavior.rs	98.07% <100.00%> (+0.12%)	⬆️

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[travis79]

Nothing to block on, just a couple of comments