Check re-exported types for status `done (untested)`

[tcharding]

Given RPC method foobar returning type FooBar with conversion error FooBarError.

Our integration testing strategy verifies that FooBar is re-exported correctly iff foobar is tested. For untested things we could at least test the re-exports.

It may be a long time until I get around to testing things that seem less important (like types with a single psbt string field since this is quite likely to be correct and can be a PITA to test).