Add checks because effects fire twice in dev for React 18

[nmathew98]

Issue: #130

Only call openChild if window is not set and only call componentWillUnmount when mounted state is true

Also remove @private modifier before import statements

@rmariuzzo

[rmariuzzo]

Will review by the EOD.

Quick update: I took a 5-days vacation. My health is average. I'm planning to add more collaborator to ensure continuous maintenance of this library.

[rmariuzzo]

Thank you @nmathew98