fix s.t. scales relative to parents even when within `mr-panel`

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Fixes #592

Problem

mr-panel flattens its children so we can't rely on object3D hierarchy for certain attributes - fixing this for scale, there will be other issues like this in future as well

Solution

add an if-check for if in mr-panel

Required to Merge

[x] 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
[x] 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. Before:
scaling not working for the relative differences

After:

big fishy is super big
little fishy is super little

https://github.com/Volumetrics-io/mrjs/assets/19377312/e757b821-42dc-406f-86ab-26c8508d2fc8

[x] 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

Volumetrics-io / mrjs

fix s.t. scales relative to parents even when within `mr-panel` #593

Linking

Problem

Solution

Required to Merge