Lazy fields that point to a specific Job

[tclose]

Lazy fields that point to a specific Job, i.e. instead of a Node, to allow execution of a node with partially resolved state arrays when the upstream hasn't completed yet, or partially errored. Note that these would not replace the current "lazy node out" fields, but be generated from them at runtime and passed to the jobs that arise from the node when they are created.

When a state is initialised and arrays are split over, if you have a LazyJobOutField (or better name), even if the full array isn't ready yet you can create an array filled with LazyJobOutField objects, which then can be resolved independently allowing downstream jobs to be executed when its immediate predecessors have finished, even if the predecessors of its sibling jobs have failed.

[effigies]

I think this should definitely be 1.1 if not 1.0. It feels like a potentially big can of worms, and I don't know how I'd tackle it myself, so I'm hesitant to put it on 1.0.