chore: remove ~50k lines of unreachable dead code (#8913)

* chore: remove unreachable dead code across the codebase

Remove ~50,000 lines of unreachable code identified by static analysis.

Major removals:
- weed/filer/redis_lua: entire unused Redis Lua filer store implementation
- weed/wdclient/net2, resource_pool: unused connection/resource pool packages
- weed/plugin/worker/lifecycle: unused lifecycle plugin worker
- weed/s3api: unused S3 policy templates, presigned URL IAM, streaming copy,
  multipart IAM, key rotation, and various SSE helper functions
- weed/mq/kafka: unused partition mapping, compression, schema, and protocol functions
- weed/mq/offset: unused SQL storage and migration code
- weed/worker: unused registry, task, and monitoring functions
- weed/query: unused SQL engine, parquet scanner, and type functions
- weed/shell: unused EC proportional rebalance functions
- weed/storage/erasure_coding/distribution: unused distribution analysis functions
- Individual unreachable functions removed from 150+ files across admin,
  credential, filer, iam, kms, mount, mq, operation, pb, s3api, server,
  shell, storage, topology, and util packages

* fix(s3): reset shared memory store in IAM test to prevent flaky failure

TestLoadIAMManagerFromConfig_EmptyConfigWithFallbackKey was flaky because
the MemoryStore credential backend is a singleton registered via init().
Earlier tests that create anonymous identities pollute the shared store,
causing LookupAnonymous() to unexpectedly return true.

Fix by calling Reset() on the memory store before the test runs.

* style: run gofmt on changed files

* fix: restore KMS functions used by integration tests

* fix(plugin): prevent panic on send to closed worker session channel

The Plugin.sendToWorker method could panic with "send on closed channel"
when a worker disconnected while a message was being sent. The race was
between streamSession.close() closing the outgoing channel and sendToWorker
writing to it concurrently.

Add a done channel to streamSession that is closed before the outgoing
channel, and check it in sendToWorker's select to safely detect closed
sessions without panicking.

weed/admin/plugin/plugin_scheduler.go

@@ -95,16 +95,6 @@ func (r *Plugin) laneSchedulerLoop(ls *schedulerLaneState) {
 	}
 }
 
-// schedulerLoop is kept for backward compatibility; it delegates to
-// laneSchedulerLoop with the default lane. New code should not call this.
-func (r *Plugin) schedulerLoop() {
-	ls := r.lanes[LaneDefault]
-	if ls == nil {
-		ls = newLaneState(LaneDefault)
-	}
-	r.laneSchedulerLoop(ls)
-}
-
 // runLaneSchedulerIteration runs one scheduling pass for a single lane,
 // processing only the job types assigned to that lane.
 //
@@ -229,82 +219,6 @@ func (r *Plugin) runLaneSchedulerIterationConcurrent(ls *schedulerLaneState, job
 	return hadJobs.Load()
 }
 
-// runSchedulerIteration is kept for backward compatibility. It runs a
-// single iteration across ALL job types (equivalent to the old single-loop
-// behavior). It is only used by the legacy schedulerLoop() fallback.
-func (r *Plugin) runSchedulerIteration() bool {
-	ls := r.lanes[LaneDefault]
-	if ls == nil {
-		ls = newLaneState(LaneDefault)
-	}
-	// For backward compat, the old function processes all job types.
-	r.expireStaleJobs(time.Now().UTC())
-
-	jobTypes := r.registry.DetectableJobTypes()
-	if len(jobTypes) == 0 {
-		r.setSchedulerLoopState("", "idle")
-		return false
-	}
-
-	r.setSchedulerLoopState("", "waiting_for_lock")
-	releaseLock, err := r.acquireAdminLock("plugin scheduler iteration")
-	if err != nil {
-		glog.Warningf("Plugin scheduler failed to acquire lock: %v", err)
-		r.setSchedulerLoopState("", "idle")
-		return false
-	}
-	if releaseLock != nil {
-		defer releaseLock()
-	}
-
-	active := make(map[string]struct{}, len(jobTypes))
-	hadJobs := false
-
-	for _, jobType := range jobTypes {
-		active[jobType] = struct{}{}
-
-		policy, enabled, err := r.loadSchedulerPolicy(jobType)
-		if err != nil {
-			glog.Warningf("Plugin scheduler failed to load policy for %s: %v", jobType, err)
-			continue
-		}
-		if !enabled {
-			r.clearSchedulerJobType(jobType)
-			continue
-		}
-		initialDelay := time.Duration(0)
-		if runInfo := r.snapshotSchedulerRun(jobType); runInfo.lastRunStartedAt.IsZero() {
-			initialDelay = 5 * time.Second
-		}
-		if !r.markDetectionDue(jobType, policy.DetectionInterval, initialDelay) {
-			continue
-		}
-
-		detected := r.runJobTypeIteration(jobType, policy)
-		if detected {
-			hadJobs = true
-		}
-	}
-
-	r.pruneSchedulerState(active)
-	r.pruneDetectorLeases(active)
-	r.setSchedulerLoopState("", "idle")
-	return hadJobs
-}
-
-// wakeLane wakes the scheduler goroutine for a specific lane.
-func (r *Plugin) wakeLane(lane SchedulerLane) {
-	if r == nil {
-		return
-	}
-	if ls, ok := r.lanes[lane]; ok {
-		select {
-		case ls.wakeCh <- struct{}{}:
-		default:
-		}
-	}
-}
-
 // wakeAllLanes wakes all lane scheduler goroutines.
 func (r *Plugin) wakeAllLanes() {
 	if r == nil {