update mrapp for cleanup and garbage collection

[hanbollar]

Linking

Related to #677
Fixes #678

Problem

Description of the problem including potential code and/or screenshots as an example

Solution

Quick explanation of change to be done

Breaking Change

If this is a breaking change describe the before and after and why the change was necessary

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Required to Merge

• PASS - all necessary actions must pass (excluding the auto-skipped ones)
• TEST IN HEADSET - main dev-testing-example and any of the other examples still work as expected
• [ ] VIDEO - if this pr changes something visually - post a video here of it in headset-MR and/or on desktop (depending on what it affects) for the reviewer to reference.
• TITLE - make sure the pr's title is updated appropriately as it will be used to name the commit on merge
• [ ] BREAKING CHANGE
  • DOCUMENTATION: This includes any changes to html tags and their components
    • make a pr in the documentation repo that updates the manual docs to match the breaking change
    • link the pr of the documentation repo here: #pr
    • that pr must be approved by @lobau
  • SAMPLES/INDEX.HTML: This includes any changes (html tags or otherwise) that must be done to our landing page submodule as an effect of this pr's updates
    • make a pr in the mrjs landing page repo that updates the landing page to match the breaking change
    • link the pr of the landing page repo here: #pr
    • that pr must be approved by @hanbollar

[render]

Your Render PR Server URL is https://examples-mrjs-pr-669.onrender.com.

Follow its progress at https://dashboard.render.com/static/srv-cp40soe3e1ms73choh2g.

[hanbollar]

need to fix 'enter/exit' MR issue - otherwise it's ready to go

[hanbollar]

swapping this back to main since it's not part of the major 'breaking-changes' refactor

[hanbollar]

cant swap - should keep sub-main as itself and then merge that in after this pr since that's still before the big refactor / breaking change