Rename DefaultConfig to DefaultPlacementRequest

Aligns with the PlacementRequest type naming for consistency

weed/storage/erasure_coding/placement/placement.go

@@ -64,8 +64,8 @@ type PlacementRequest struct {
 	PreferDifferentRacks bool
 }
 
-// DefaultConfig returns the default placement configuration
-func DefaultConfig() PlacementRequest {
+// DefaultPlacementRequest returns the default placement configuration
+func DefaultPlacementRequest() PlacementRequest {
 	return PlacementRequest{
 		ShardsNeeded:           14,
 		MaxShardsPerServer:     0,

weed/storage/erasure_coding/placement/placement_test.go

@@ -336,7 +336,7 @@ func TestSelectDestinations_NoSuitableDisks(t *testing.T) {
 }
 
 func TestSelectDestinations_EmptyInput(t *testing.T) {
-	config := DefaultConfig()
+	config := DefaultPlacementRequest()
 	_, err := SelectDestinations([]*DiskCandidate{}, config)
 	if err == nil {
 		t.Error("expected error for empty input, got nil")