avoid repeated large allocations for large parts (#17968)

objects with 10,000 parts and many of them can
cause a large memory spike which can potentially
lead to OOM due to lack of GC.

with previous PR reducing the memory usage significantly
in #17963, this PR reduces this further by 80% under
repeated calls.

Scanner sub-system has no use for the slice of Parts(),
it is better left empty.

```
benchmark                            old ns/op     new ns/op     delta
BenchmarkToFileInfo/ToFileInfo-8     295658        188143        -36.36%

benchmark                            old allocs     new allocs     delta
BenchmarkToFileInfo/ToFileInfo-8     61             60             -1.64%

benchmark                            old bytes     new bytes     delta
BenchmarkToFileInfo/ToFileInfo-8     1097210       227255        -79.29%
```

cmd/xl-storage-format-utils_test.go

@@ -175,7 +175,7 @@ func TestGetFileInfoVersions(t *testing.T) {
 	if err != nil {
 		t.Fatalf("Failed to serialize xlmeta %v", err)
 	}
-	fivs, err := getFileInfoVersions(buf, basefi.Volume, basefi.Name)
+	fivs, err := getFileInfoVersions(buf, basefi.Volume, basefi.Name, true)
 	if err != nil {
 		t.Fatalf("getFileInfoVersions failed: %v", err)
 	}