Currently, a node either supports lazyness during execution (like the Switch
node), or it doesn't. If it does support lazyness, then every input is computed
lazily. However, usually not all inputs actually have to be computed lazily.
E.g. the boolean switch input is always required, while the other inputs
should be computed lazily.
Better support for such sockets can avoid unnecessary round trips through
the node execution function.
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