fix(live-sample): fix live samples for safari

[fiji-flo]

Summary

Lazy loading is tricky. Let's be more defensive.

This hopefully resolves #10764

Problem

It looked like we were hitting a weird race condition in Safari.

Checking for the source and removing the eventListener should only improve things. This also sets the initialized flag in the runner earlier to avoid races.

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How did you test this change?

Locally but it's hard to reproduce. Setting:

BUILD_LIVE_SAMPLES_BASE_URL=https://live.mdnyalp.dev

and disabling caching helps.

[caugner]

Converted to draft, as it doesn't resolve the issue (verified by deploying to stage).

[github-actions[bot]]

This pull request has merge conflicts that must be resolved before it can be merged.