Edit: Flush diffs on apply

[umpox]

closes #2082

Description

Diffs can be scheduled - these update decorations, but this can conflict with removing the decorations when a task is applied.

So we have a race condition where it is possible that:

1. The task is applied, and decorations are removed
2. Later, a scheduled diff updates and re-applies the old decorations

To work around this, we just ensure that any scheduled diff updates are ran before we finally remove all decorations

Test plan

1. Run an edit

2. Confirm that decorations are not shown on apply

3. Run the /doc command

4. Confirm that decorations are not shown on apply

[philipp-spiess]