Tool to convert API workflows to typed Rust code

[philpax]

API workflows need to be manually converted to their typed Rust representation (or untyped dynamic, as it may be). This is not that difficult, but it can be quite tedious. It should be possible to automate this by loading the workflow in, converting all of the nodes to Rust nodes, and then collapsing the nodes with outdegree 1.

There is some interaction with #6 here - we need to know which nodes have typed representations to do this correctly. We could always assume that all non-standard types are dynamic, but that may not always be the case. Additionally, we'd need to convey information about which nodes are available anyway - the refactoring associated with #6 should expose this information.