[Tests] Add unit tests for stringifyFilters in notifications-system

[gonzaloriestra]

WHY are these changes introduced?

The stringifyFilters function in packages/cli-kit/src/public/node/notifications-system.ts lacked unit test coverage. Adding tests ensures filter formatting for dates, versions, frequencies, surfaces, and commands remains stable and correct.

WHAT is this pull request doing?

• Adds unit tests for stringifyFilters covering:
  • Empty filter options
  • All filter criteria (min/max date, min/max version, frequency, surface, commands)
  • Specific frequency cases (once, once_a_week, once_a_day)

How to test your changes?

CI

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PR created automatically by Jules for task 7348883676509157134 started by @gonzaloriestra

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