fix: stub out the FileSize command so lotus libraries can build on Windows

storage/sealer/fsutil/filesize_unix.go

@@ -1,3 +1,6 @@
+//go:build !windows
+// +build !windows
+
 package fsutil
 
 import (

storage/sealer/fsutil/filesize_windows.go

@@ -0,0 +1,16 @@
+package fsutil
+
+import (
+	"fmt"
+)
+
+type SizeInfo struct {
+	OnDisk int64
+}
+
+// FileSize returns bytes used by a file or directory on disk
+// NOTE: We care about the allocated bytes, not file or directory size
+// This is not currently supported on Windows, but at least other lotus can components can build on Windows now
+func FileSize(path string) (SizeInfo, error) {
+	return SizeInfo{0}, fmt.Errorf("unsupported")
+}