Import persistent notification (part 5)

[emontnemery]

Proposed change

Import persistent_notification (part 5)

By importing instead of accessing via hass.components, type checking etc. works correctly

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[epenet]

Code LGTM - just a small note about the tests

[epenet]

I'm not sure why this change slipped into this PR

[emontnemery]

The constant was moved in part1 (#63898) to fix a circular import, this just updates the import.