ec: add diskType parameter to core EC functions

Add diskType parameter to:
- ecBalancer struct
- collectEcVolumeServersByDc()
- collectEcNodesForDC()
- collectEcNodes()
- EcBalance()

This allows EC operations to target specific disk types (hdd, ssd, etc.)
instead of being hardcoded to HardDriveType only.

For backward compatibility, all callers currently pass types.HardDriveType
as the default value. Subsequent commits will add -diskType flags to
the individual EC commands.

weed/shell/command_ec_balance.go

@@ -4,6 +4,8 @@ import (
 	"flag"
 	"fmt"
 	"io"
+
+	"github.com/seaweedfs/seaweedfs/weed/storage/types"
 )
 
 func init() {
@@ -67,5 +69,5 @@ func (c *commandEcBalance) Do(args []string, commandEnv *CommandEnv, writer io.W
 		return err
 	}
 
-	return EcBalance(commandEnv, collections, *dc, rp, *maxParallelization, *applyBalancing)
+	return EcBalance(commandEnv, collections, *dc, rp, types.HardDriveType, *maxParallelization, *applyBalancing)
 }