chore: readd data.lua but deprecate it

lua/auto-save/utils/data.lua

@@ -0,0 +1,20 @@
+--- @deprecated
+local M = {}
+
+--- @deprecated
+function M.set_of(list)
+  local set = {}
+  for i = 1, #list do
+    set[list[i]] = true
+  end
+  return set
+end
+
+--- @deprecated
+function M.not_in(var, arr)
+  if M.set_of(arr)[var] == nil then
+    return true
+  end
+end
+
+return M