fix(platform): support Windows storage and native filesystem boundaries

internal/fileutil/space_unix.go

@@ -0,0 +1,14 @@
+//go:build !windows
+
+package fileutil
+
+import "syscall"
+
+// AvailableBytes returns disk space available to the current user.
+func AvailableBytes(dir string) (uint64, error) {
+	var stat syscall.Statfs_t
+	if err := syscall.Statfs(dir, &stat); err != nil {
+		return 0, err
+	}
+	return stat.Bavail * uint64(stat.Bsize), nil
+}