refactor(datetime): replace enum with object

[realpha]

This PR replaces the used typescript enum in the datetime module with a
as const object as requested here

As this enum is only used internally, merging this change wouldn't constitute a
breaking change.

History:

• chore(root): ignore .tool-versions
• feat(datetime): replace enum with const object

[CLAassistant]

All committers have signed the CLA.

[iuioiua]

LGTM! Thank you 🙏🏾