Add helper functions for checking/setting invite expiration

[rdimitrov]

Summary

The following PR adds helper functions for checking/setting invite expiration. Also sets the const scope to local as they are not really meant to be used in other way.

Split from #3689

Change Type

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• Bug fix (resolves an issue without affecting existing features)
• Feature (adds new functionality without breaking changes)
• Breaking change (may impact existing functionalities or require documentation updates)
• Documentation (updates or additions to documentation)
• Refactoring or test improvements (no bug fixes or new functionality)

Testing

Outline how the changes were tested, including steps to reproduce and any relevant configurations.
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Review Checklist:

• Reviewed my own code for quality and clarity.
• Added comments to complex or tricky code sections.
• Updated any affected documentation.
• Included tests that validate the fix or feature.
• Checked that related changes are merged.

[coveralls]

coverage: 52.731% (-0.02%) from 52.752%
when pulling 8b4a693 on inv
into 07fc788 on main.

[coveralls]

coverage: 52.727% (-0.03%) from 52.752%
when pulling 63b2e6b on inv
into 07fc788 on main.