* chore - move chat session service implementation and interface into their own files
* chore - move chat saving service implementation and interface into their own files
* - move hunks into session (instead of strategy)
- recompute them after receiving AI changes
- accept& discard moves hunks from textModelN to textModel0 and vice versa
- service renames
- tests
* - session doesn't know about an editor, only service does
- allow to "move" session to a different editor
- let controller pickup session after move to its editor
- session saving picks up orphand sessions
* try to restore editors when group is still valid
* ctrl - don't pause when cancellation happens during session create
* fix tests
