Fix opacity attributes from defaulting to 0 rather than 1

[Keavon]

Fixes a regression introduced in 62203cb where the Painted Dreams demo artwork's "Top Right Black - Dots" and "Bottom Black - Dots" layers had a 0 opacity.

[gemini-code-assist]

Code Review

This pull request introduces implicit attribute defaults for list attributes in node-graph/libraries/core-types/src/list.rs, specifically defaulting opacity attributes to 1.0 (fully opaque) instead of the type's default 0.0 to prevent items from vanishing during list operations. The feedback focuses on performance optimizations: first, optimizing pad_with_implicit_default by downcasting to Attribute<f64> and using Vec::resize to avoid excessive heap allocations and dynamic dispatch; second, pre-allocating vectors with appropriate capacities in into_attribute and new_attribute_padded to prevent unnecessary reallocations.

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[cubic-dev-ai]

1 issue found across 1 file

Confidence score: 5/5

• This looks low risk and safe to merge: the reported issue in node-graph/libraries/core-types/src/list.rs is a small performance optimization rather than a correctness or user-facing bug.
• The suggestion to use Vec::with_capacity(preceding_defaults + 1) instead of Vec::new() reduces potential reallocations during padding/push, but does not indicate functional breakage.
• Pay close attention to node-graph/libraries/core-types/src/list.rs - preallocating vector capacity can avoid unnecessary reallocations in this code path.

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