Remove the conversion to and from `CurveEval` by supporting the
new Curves data-block in the node. This allows for some simplifications
to the code, as well as a fix for transfering curve domain attributes
when duplicating the curve domain.
The performance improvements (obverved through the timings overlay)
can be relatively massive with many curves. When duplicating 10000
4-point curves to become 2 million curves, I observed an approximate
150x improvement, from about 3 seconds to about 20ms.
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