Prepare process_runs for pipelines migration (#3675)

* Drop unrechable non-services code in _handle_run_replicas

* Add more process_runs tests

* Refactor _process_active_run loop

* Document analysis classes

* Fix implicit RunStatus.PENDING

* Replace unhandled ValueError with ServerError and fix broken assert

* Drop lazy imports

* Drop redundant except Exception

* Drop dummy non-services code in _handle_run_replicas

* Extracted _terminate_removed_replica_groups

* Drop redundant replicas arg from _update_jobs_to_new_deployment_in_place

* Minor renaming

* Extract get_group_rollout_state

* Move run job lookup into analysis

Author: r4victor