custom task routing

[koaning (Vincent D Warmerdam)]

Note that this issue was patched in the new alpha release of this week.

Prodigy 1.12 alpha release: LLM-assisted workflows, prompt engineering & fully custom task routing for multi-annotator scenarios.

UPDATE: v1.12a4 has been released which fixes issues with the task router and session factory. It also adds a new progress estimator which is based on the relative position in the source object. The motivation for this new way of estimating progress was to provide a more reliable estimate when the actual total target is unknown while working with the stream of data. Since it is very different from the progress based on the number of annotated examples, we now distinguish in the UI between targ…