Master: volume assignment concurrency (#7159)

* volume assginment concurrency

* accurate tests

* ensure uniqness

* reserve atomically

* address comments

* atomic

* ReserveOneVolumeForReservation

* duplicated

* Update weed/topology/node.go

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* Update weed/topology/node.go

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

* atomic counter

* dedup

* select the appropriate functions based on the useReservations flag

---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

weed/topology/rack.go

@@ -1,12 +1,13 @@
 package topology
 
 import (
-	"github.com/seaweedfs/seaweedfs/weed/pb/master_pb"
-	"github.com/seaweedfs/seaweedfs/weed/storage/types"
-	"github.com/seaweedfs/seaweedfs/weed/util"
 	"slices"
 	"strings"
 	"time"
+
+	"github.com/seaweedfs/seaweedfs/weed/pb/master_pb"
+	"github.com/seaweedfs/seaweedfs/weed/storage/types"
+	"github.com/seaweedfs/seaweedfs/weed/util"
 )
 
 type Rack struct {
@@ -19,6 +20,7 @@ func NewRack(id string) *Rack {
 	r.nodeType = "Rack"
 	r.diskUsages = newDiskUsages()
 	r.children = make(map[NodeId]Node)
+	r.capacityReservations = newCapacityReservations()
 	r.NodeImpl.value = r
 	return r
 }