Add eink_optimization_spec

spec/unit/eink_optimization_spec.lua

@@ -0,0 +1,8 @@
+require("commonrequire")
+
+describe("eink optimization setting", function()
+    it("should be correctly loaded", function()
+        G_reader_settings:saveSetting("eink", true)
+        assert.Equals(require("device").screen.eink, true)
+    end)
+end)