Make the Gate event based.

[nicolas-rabault]

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PR Description section

Description and dependencies

Please include here a summary of the changes and the related issue. List any dependencies that are required for this change.

Changes

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• New feature (non-breaking change which adds functionality)

Related issue(s)

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Developer section

• [Documentation] is up to date with new feature
• [Tests] are passed OK (non regression, new features & bug fixes)
• [Code Quality] please check if:
  • Each function has a header (description, inputs, outputs)
  • Code is commented (particularly in hard to understand areas)
  • There are no new warnings that can be corrected
  • Commits policy is respected (constitancy commits, clear commits comments)

QA section

• [Review] tests for new features have been reviewed
• [Changelog] is up-to-date with expected tags
  🆕 Feature: [Feature] Description...
  🆕 Added: [Feature] Description...
  🆕 Changed: [Feature] Description...
  🛠️ Fix: [Feature] Description...