fix: Hitbox children of a CompositeHitbox to return correct parent

[spydon]

Description

Since the CompositeHitbox shouldn't be counted as the real parent of a hitbox this PR ignores it for setting the hitboxParent, which is used to report the other component's parent in the onCollision* callbacks.

Checklist

• [x] The title of my PR starts with a Conventional Commit prefix (fix:, feat:, docs: etc).
• [x] I have followed the Contributor Guide when preparing my PR.
• [x] I have updated/added tests for ALL new/updated/fixed functionality.
• [x] I have updated/added relevant documentation in docs and added dartdoc comments with ///.
• [x] I have updated/added relevant examples in examples or docs.

Breaking Change?

• [x] No, this PR is not a breaking change.

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