The series overhauls the compaction_manager::task design and implementation
by properly layering the functionality between the compaction_manager
that deals with generic task execution, and the per-task business logic that is defined
in a set of classes derived from the generic task class.
While at it, the series introduces `task::state` and a set of helper functions to manage it
to prevent leaks in the statistics, fixing #9974.
Two more stats counter were exposed: `completed_tasks` and a new `postponed_tasks`.
Test: sstable_compaction_test
Dtest: compaction_test.py compaction_additional_test.py
Fixes#9974Closes#10122
* github.com:scylladb/scylla:
compaction_manager: use coroutine::switch_to
compaction_manager::task: drop _compaction_running
compaction_manager: move per-type logic to derived task
compaction_manager: task: add state enum
compaction_manager: task: add maybe_retry
compaction_manager: reevaluate_postponed_compactions: mark as noexcept
compaction_manager: define derived task types
compaction_manager: register_metrics: expose postponed_compactions
compaction_manager: register_metrics: expose failed_compactions
compaction_manager: register_metrics: expose _stats.completed_tasks
compaction: add documentation for compaction_type to string conversions
compaction: expose to_string(compaction_type)
compaction_manager: task: standardize task description in log messages
compaction_manager: refactor can_proceed
compaction_manager: pass compaction_manager& to task ctor
compaction_manager: use shared_ptr<task> rather than lw_shared_ptr
compaction_manager: rewrite_sstables: acquire _maintenance_ops_sem once
compaction_manager: use compaction_state::lock only to synchronize major and regular compaction
7e0b51ff23