Split the single plugin scheduler loop into independent per-lane
goroutines so that volume management, iceberg compaction, and lifecycle
operations never block each other.
Each lane has its own:
- Goroutine (laneSchedulerLoop)
- Wake channel for immediate scheduling
- Admin lock scope (e.g. "plugin scheduler:default")
- Configurable idle sleep duration
- Loop state tracking
Three lanes are defined:
- default: vacuum, volume_balance, ec_balance, erasure_coding, admin_script
- iceberg: iceberg_maintenance
- lifecycle: s3_lifecycle (new, handler coming in a later commit)
Job types are mapped to lanes via a hardcoded map with LaneDefault as
the fallback. The SchedulerJobTypeState and SchedulerStatus types now
include a Lane field for API consumers.
e3e015e108