Input: Process input events in batches (#7483)

Requires https://github.com/koreader/koreader-base/pull/1344 & https://github.com/koreader/koreader-base/pull/1346 (fix #7485)

Assorted input fixes:

* Actually handle errors in the "there's a callback timer" input polling loop.
* Don't break timerfd when the clock probe was inconclusive.

Not directly related, but noticed because of duplicate onInputEvent handlers:

* HookContainer: Fix deregistration to actually deregister properly. "Regression" extant since its inception in #2933 (!).
* Made sure the three plugins (basically the trio of AutoThingies ;p) that were using HookContainer actually unschedule their task on teardown.

frontend/ui/hook_container.lua

@@ -49,16 +49,18 @@ end
 function HookContainer:registerWidget(name, widget)
     self:_assertIsValidName(name)
     assert(type(widget) == "table")
-    self:register(name, function(args)
+    -- *That* is the function we actually register and need to unregister later, so keep a ref to it...
+    local hook_func = function(args)
         local f = widget["on" .. name]
         self:_assertIsValidFunction(f)
         f(widget, args)
-    end)
+    end
+    self:register(name, hook_func)
     local original_close_widget = widget.onCloseWidget
     self:_assertIsValidFunctionOrNil(original_close_widget)
     widget.onCloseWidget = function()
         if original_close_widget then original_close_widget(widget) end
-        self:unregister(name, widget["on" .. name])
+        self:unregister(name, hook_func)
     end
 end