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/credential/config_loader.go

@@ -57,42 +57,6 @@ func LoadCredentialConfiguration() (*CredentialConfig, error) {
 	}, nil
 }
 
-// GetCredentialStoreConfig extracts credential store configuration from command line flags
-// This is used when credential store is configured via command line instead of credential.toml
-func GetCredentialStoreConfig(store string, config util.Configuration, prefix string) *CredentialConfig {
-	if store == "" {
-		return nil
-	}
-
-	return &CredentialConfig{
-		Store:  store,
-		Config: config,
-		Prefix: prefix,
-	}
-}
-
-// MergeCredentialConfig merges command line credential config with credential.toml config
-// Command line flags take priority over credential.toml
-func MergeCredentialConfig(cmdLineStore string, cmdLineConfig util.Configuration, cmdLinePrefix string) (*CredentialConfig, error) {
-	// If command line credential store is specified, use it
-	if cmdLineStore != "" {
-		glog.V(0).Infof("Using command line credential configuration: store=%s", cmdLineStore)
-		return GetCredentialStoreConfig(cmdLineStore, cmdLineConfig, cmdLinePrefix), nil
-	}
-
-	// Otherwise, try to load from credential.toml
-	config, err := LoadCredentialConfiguration()
-	if err != nil {
-		return nil, err
-	}
-
-	if config == nil {
-		glog.V(1).Info("No credential store configured")
-	}
-
-	return config, nil
-}
-
 // NewCredentialManagerWithDefaults creates a credential manager with fallback to defaults
 // If explicitStore is provided, it will be used regardless of credential.toml
 // If explicitStore is empty, it tries credential.toml first, then defaults to "filer_etc"