* Rename "editor:layer" to "editor:layer_path" and centralize it in a const
* Centralize "editor:merged_layers" in a const
* Centralize all other attributes in consts
* Rename consts with ATTR_ prefix
* Format
* Feature-gate serde derives behind cfg_attr in all runtime node graph type crates
* Refactor Table to move its hard-coded fields into an attributes field
* Encapsulate TableRow/TableRowRef/TableRowMut attribute fields behind accessor methods
* Remove TaggedValue::GraphicUnused
* Refactor Table<T> to use dynamic attributes instead fixed names
* Fix code review soundness concerns
* Add todo work
* Replace row-oriented Table<T> API with column-oriented access
* Fix attribute propagation bugs
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