fix: close volumes and EC shards in tests for Windows compatibility (#8152)

* fix: close volumes and EC shards in tests to prevent Windows cleanup failures

On Windows, t.TempDir() cleanup fails when test files are still open
because Windows enforces mandatory file locking. Add defer v.Close(),
defer store.Close(), and EC volume cleanup to ensure all file handles
are released before temp directory removal.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* refactor: extract closeEcVolumes helper to reduce duplication

Address code review feedback by extracting the repeated EC volume
cleanup loop into a closeEcVolumes() helper function.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

weed/storage/volume_write_test.go

@@ -21,6 +21,7 @@ func TestSearchVolumesWithDeletedNeedles(t *testing.T) {
 	if err != nil {
 		t.Fatalf("volume creation: %v", err)
 	}
+	defer v.Close()
 
 	count := 20
 
@@ -119,6 +120,7 @@ func TestDestroyNonemptyVolumeWithOnlyEmpty(t *testing.T) {
 	if err != nil {
 		t.Fatalf("volume creation: %v", err)
 	}
+	defer v.Close()
 	path := v.DataBackend.Name()
 
 	// should return "volume not empty" error and do not delete file when Destroy non-empty volume