feat(s3/lifecycle): expose Prometheus metrics (Phase 7) (#9375)

* feat(s3/lifecycle): expose Prometheus metrics (Phase 7)

Five new gauges/counters under the s3_lifecycle subsystem so operators
can see what the worker is doing without grepping logs:

- dispatch_total{bucket,kind,outcome} — every LifecycleDelete RPC
  bumps this. Outcome is the proto enum name (DONE, NOOP_RESOLVED,
  RETRY_LATER, BLOCKED, …) plus a synthetic "RPC_ERROR" for transport
  failures classified as RETRY_LATER.
- schedule_depth{shard} — pending matches in each shard's schedule,
  sampled on the dispatcher tick.
- cursor_min_ts_ns{shard} — per-shard min cursor timestamp; lag is
  derived as (now - min) by the scrape side.
- events_total{shard} — meta-log events the reader fed to the router.
- bootstrap_dispatch_total{bucket,kind} — bootstrap-walk dispatches.

Test asserts the dispatch counter increments for both DONE and
RPC_ERROR paths.

* fix(stats): purge lifecycle bucket label series in DeleteBucketMetrics

The two new bucket-labeled lifecycle counters
(S3LifecycleDispatchCounter, S3LifecycleBootstrapDispatchCounter)
weren't included in DeleteBucketMetrics, so explicit bucket teardown
left their label series behind — same cardinality leak the existing
counters above already avoid. Tack them onto the same DeletePartialMatch
chain.

weed/s3api/s3lifecycle/bootstrap/walker.go

@@ -15,6 +15,7 @@ import (
 	"github.com/seaweedfs/seaweedfs/weed/glog"
 	"github.com/seaweedfs/seaweedfs/weed/s3api/s3lifecycle"
 	"github.com/seaweedfs/seaweedfs/weed/s3api/s3lifecycle/engine"
+	"github.com/seaweedfs/seaweedfs/weed/stats"
 )
 
 // Entry is the routing-relevant slice of a filer entry. SuccessorModTime
@@ -160,6 +161,7 @@ func walkEntry(ctx context.Context, snap *engine.Snapshot, bucket string, entry
 				bucket, entry.Path, key.ActionKind, err)
 			return err
 		}
+		stats.S3LifecycleBootstrapDispatchCounter.WithLabelValues(bucket, key.ActionKind.String()).Inc()
 	}
 	return nil
 }