[feat, Kobo] Autoshutdown (#5335)

The methods used here will likely work on most embedded devices, which is why I put them in their own WakeupMgr interface/scheduler module, separate from Kobo.

See https://www.mobileread.com/forums/showthread.php?p=3886403#post3886403 for more context.

Fixes #3806.

spec/unit/wakeupmgr_spec.lua

@@ -0,0 +1,55 @@
+describe("WakeupMgr", function()
+    local RTC
+    local WakeupMgr
+    local epoch1, epoch2, epoch3
+
+    setup(function()
+        require("commonrequire")
+        package.unloadAll()
+        RTC = require("ffi/rtc")
+        WakeupMgr = require("device/wakeupmgr")
+        -- We could theoretically test this by running the tests as root locally.
+        stub(WakeupMgr, "setWakeupAlarm")
+        WakeupMgr.validateWakeupAlarmByProximity = spy.new(function() return true end)
+
+        epoch1 = RTC:secondsFromNowToEpoch(1234)
+        epoch2 = RTC:secondsFromNowToEpoch(123)
+        epoch3 = RTC:secondsFromNowToEpoch(9999)
+    end)
+
+    it("should add a task", function()
+        WakeupMgr:addTask(1234, function() end)
+        assert.is_equal(epoch1, WakeupMgr._task_queue[1].epoch)
+        assert.stub(WakeupMgr.setWakeupAlarm).was.called(1)
+    end)
+    it("should add a task in order", function()
+        WakeupMgr:addTask(9999, function() end)
+        assert.is_equal(epoch1, WakeupMgr._task_queue[1].epoch)
+        assert.stub(WakeupMgr.setWakeupAlarm).was.called(1)
+
+        WakeupMgr:addTask(123, function() end)
+        assert.is_equal(epoch2, WakeupMgr._task_queue[1].epoch)
+        assert.stub(WakeupMgr.setWakeupAlarm).was.called(2)
+    end)
+    it("should execute top task", function()
+        assert.is_true(WakeupMgr:wakeupAction())
+    end)
+    it("should have removed executed task from stack", function()
+        assert.is_equal(epoch1, WakeupMgr._task_queue[1].epoch)
+        assert.is_equal(epoch3, WakeupMgr._task_queue[2].epoch)
+    end)
+    it("should have scheduled next task after execution", function()
+        assert.stub(WakeupMgr.setWakeupAlarm).was.called(3)
+    end)
+    it("should remove arbitrary task from stack", function()
+        WakeupMgr:removeTask(2)
+        assert.is_equal(epoch1, WakeupMgr._task_queue[1].epoch)
+        assert.is_equal(nil, WakeupMgr._task_queue[2])
+    end)
+    it("should execute last task", function()
+        assert.is_true(WakeupMgr:wakeupAction())
+    end)
+    it("should not have scheduled a wakeup without a task", function()
+        assert.stub(WakeupMgr.setWakeupAlarm).was.called(3)
+    end)
+end)