Stop flatten_graphic_list() from adding unused attributes

[Keavon]

After a node such as Flatten Vector, we don't have transform, opacity, opacity_fill, etc. being added as attributes that were not part of the input data.

[gemini-code-assist]

Code Review

This pull request modifies the flatten_graphic_list function in graphic.rs to ensure that parent attributes (such as transform, opacity, fill, and layer path) are only composed onto children if the parent actually carries those attributes. This prevents the flattening process from inventing attribute columns that neither the parent nor the child originally possessed. Additionally, unit tests have been added to verify this behavior. There are no review comments to address, and the changes look solid.

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[cubic-dev-ai]

No issues found across 1 file

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Re-trigger cubic}