refactor: extract EC orchestration into a shared weed/ec package (#10760)

* shell: move ErrorWaitGroup to weed/util

* shell: remove unused CandidateEcNode and EcRack types

* ec: extract EC orchestration logic from weed/shell into weed/ec

Move the EC node/topology model, balance engine, encode pipeline, decode
pipeline, and rebuild engine into a new weed/ec package so shell commands
and maintenance workers can share the logic. Shell commands keep flag
parsing and delegate through a small ec.Env (dial option, topology fetch,
volume locations, lock check). Tests move along with the code.

* shell: remove unused proportional-rebalance type stubs

* ec: move scrub, replication check, and shard unmount engines into weed/ec

* worker: share the EC generation-aware shard counter from weed/ec

* ec: gofmt

* shell: drop EC aliases with no remaining callers

* ec: guard a missing topology hook and nil disk entries in topology helpers

* ec: drop trailing newlines from decode error strings

* ec: re-check the shell lock before applying shard unmounts

* shell: trim -node entries in ec.scrub

weed/shell/command_ec_common_test.go

@@ -1,51 +0,0 @@
-package shell
-
-import (
-	"testing"
-
-	"github.com/seaweedfs/seaweedfs/weed/pb/master_pb"
-	"github.com/seaweedfs/seaweedfs/weed/storage/needle"
-	"github.com/seaweedfs/seaweedfs/weed/storage/types"
-	"github.com/stretchr/testify/assert"
-)
-
-// countFreeShardSlots must report zero for a physically near-full disk even
-// though its slot math (MaxVolumeCount - VolumeCount) says it has room, so EC
-// placement never piles shards onto a full disk. Mirrors the volume #10160 gate.
-func TestCountFreeShardSlotsPhysicalDiskGate(t *testing.T) {
-	const gb = uint64(1) << 30
-
-	mk := func(total, free uint64) *master_pb.DataNodeInfo {
-		return &master_pb.DataNodeInfo{
-			Id: "n1",
-			DiskInfos: map[string]*master_pb.DiskInfo{
-				"": {MaxVolumeCount: 100, VolumeCount: 0, DiskTotalBytes: total, DiskFreeBytes: free},
-			},
-		}
-	}
-
-	// Physically empty: slot math applies, positive free slots.
-	if got := countFreeShardSlots(mk(1000*gb, 900*gb), types.HardDriveType); got <= 0 {
-		t.Errorf("physically empty disk free shard slots = %d, want > 0", got)
-	}
-	// Physically 96% full: gated to zero regardless of slot room.
-	if got := countFreeShardSlots(mk(1000*gb, 40*gb), types.HardDriveType); got != 0 {
-		t.Errorf("physically full disk free shard slots = %d, want 0", got)
-	}
-	// No byte report (older server): fall back to slot math, positive.
-	if got := countFreeShardSlots(mk(0, 0), types.HardDriveType); got <= 0 {
-		t.Errorf("unreported-bytes disk free shard slots = %d, want > 0 (slot fallback)", got)
-	}
-}
-
-func TestParseVolumeIdsFlag(t *testing.T) {
-	vids, err := parseVolumeIdsFlag("101, 102,101, 103")
-	assert.NoError(t, err)
-	assert.Equal(t, []needle.VolumeId{101, 102, 103}, vids)
-
-	_, err = parseVolumeIdsFlag("101,abc")
-	assert.Error(t, err)
-
-	_, err = parseVolumeIdsFlag(" , ")
-	assert.Error(t, err)
-}