Maybe support custom components inline

[jonnor]

Right now all components must be existing in the runtime. For testing-specific components, it could maybe be nice to optionally allow these to be defined inline in the definition of the tests.

[jonnor]

These would have to be communicated over the FBP runtime protocol using component:setsource.
Would have to check for that capability also.

https://flowbased.github.io/fbp-protocol/