Cursors for everything!

The major change in this release is that persisters and fetchers now operate on cursors instead of channels.
This means that every state change applications will go through a cursor, making the api more consistent.

This also enables a fix that ensures state changes are applied in succession. This was needed in cases where several cursor.replace/cursor.set calls were done in the same render tick, and the slowest of those calls had a potential to overwrite state changes that the fast one did. Now the complexity of that is inside of StateTrooper, ensuring that a cursor never tries to set anything with out of date state.