Link/CID AOT Validation

[bdehaynin]

Summary

For deterministic wasm, we should verify all links as part of the ahead-of-time "compilation" of workflows before any execution takes place. We should fail the workflow and return errors for all CIDs that do not exist at the time of execution.

If links do exist on the network but are not local, we should stream in the necessary (IPLD) blocks over the network to make the execution feasible, which is related to #78.

This does not involve the coordination piece of who should actually run the workflow, but only at the point when a node is deemed ready to execute it.