fix: Fixed update Interpolation incorrect with child actors

[eonarheim]

===:clipboard: PR Checklist :clipboard:===

• 📌 issue exists in github for these changes
• 🔬 existing tests still pass
• 🙈 code conforms to the style guide
• 📐 new tests written and passing / old tests updated with new scenario(s)
• 📄 changelog entry added (or not needed)

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This PR fixes an unreleased issue where fixed step update interpolation was incorrect with child actors. The issue was global and local positions were mixed in the interpolate.

Changes:

• Switch interpolation to use local positions for start and end