shell: default batch size for ec.encode and ec.decode (#10308)

* shell: ec.encode batches 10 volumes by default

Encoding a whole collection as one batch means a late failure leaves
everything half-converted. Default -batchSize to 10 so each batch is
encoded, rebalanced, verified, and its originals deleted before the
next starts. -batchSize=0 keeps the all-at-once behavior. Batch
progress messages now print only when there is more than one batch,
so small runs read as before.

* shell: ec.decode decodes in batches, refreshing topology in between

ec.decode walked every volume off the single topology snapshot taken
at startup, which goes stale as earlier decodes move shards around and
create volumes. Decode 10 volumes per batch by default, re-collecting
the topology and rebuilding the free-space accounting between batches.
-batchSize=0 keeps the single-snapshot behavior.

weed/shell/command_ec_encode_test.go

@@ -262,16 +262,16 @@ func TestParseEcEncodeVolumeIds(t *testing.T) {
 	assert.Error(t, err)
 }
 
-func TestChunkEcEncodeVolumeIds(t *testing.T) {
+func TestChunkVolumeIds(t *testing.T) {
 	vids := []needle.VolumeId{101, 102, 103, 104, 105}
 
 	assert.Equal(t, [][]needle.VolumeId{
 		{101, 102},
 		{103, 104},
 		{105},
-	}, chunkEcEncodeVolumeIds(vids, 2))
+	}, chunkVolumeIds(vids, 2))
 
-	assert.Equal(t, [][]needle.VolumeId{vids}, chunkEcEncodeVolumeIds(vids, 0))
+	assert.Equal(t, [][]needle.VolumeId{vids}, chunkVolumeIds(vids, 0))
 }
 
 func ecShardVisibilityTestTopology(nodes ...*master_pb.DataNodeInfo) *master_pb.TopologyInfo {