Clarify the reason why we need to deepcopy cached children

autoload/fern/internal/node.vim

@@ -81,9 +81,10 @@ function! fern#internal#node#children(node, provider, token, ...) abort
   if a:node.status is# s:STATUS_NONE
     return s:Promise.reject('leaf node does not have children')
   elseif has_key(a:node.concealed, '__cache_children') && options.cache
+    " Return a fresh copy of cached children so that status won't be cached
     return s:AsyncLambda.map(
           \ a:node.concealed.__cache_children,
-          \ { v -> extend(v, { 'status': v.status > 0 }) },
+          \ { v -> deepcopy(v) },
           \)
   elseif has_key(a:node.concealed, '__promise_children')
     return a:node.concealed.__promise_children