refactor: move render() to Activity super class, use freeRTOS notification (#774)

Currently, each activity has to manage their own `displayTaskLoop` which
adds redundant boilerplate code. The loop is a wait loop which is also
not the best practice, as the `updateRequested` boolean is not protected
by a mutex.

In this PR:
- Move `displayTaskLoop` to the super `Activity` class
- Replace `updateRequested` with freeRTOS's [direct to task
notification](https://www.freertos.org/Documentation/02-Kernel/02-Kernel-features/03-Direct-to-task-notifications/01-Task-notifications)
- For `ActivityWithSubactivity`, whenever a sub-activity is present, the
parent's `render()` automatically goes inactive

With this change, activities now only need to expose `render()`
function, and anywhere in the code base can call `requestUpdate()` to
request a new rendering pass.

In theory, this change may also make the battery life a bit better,
since one wait loop is removed. Although the equipment in my home lab
wasn't been able to verify it (the electric current is too noisy and
small). Would appreciate if anyone has any insights on this subject.

Update: I managed to hack [a small piece of
code](https://github.com/ngxson/crosspoint-reader/tree/xsn/measure_cpu_usage)
that allow tracking CPU idle time.

The CPU load does decrease a bit (1.47% down to 1.39%), which make
sense, because the display task is now sleeping most of the time unless
notified. This should translate to a slightly increase in battery life
in the long run.

```
PR:
[40012] [MEM] Free: 185856 bytes, Total: 231004 bytes, Min Free: 123316 bytes
[40012] [IDLE] Idle time: 98.61% (CPU load: 1.39%)
[50017] [MEM] Free: 185856 bytes, Total: 231004 bytes, Min Free: 123316 bytes
[50017] [IDLE] Idle time: 98.61% (CPU load: 1.39%)
[60022] [MEM] Free: 185856 bytes, Total: 231004 bytes, Min Free: 123316 bytes
[60022] [IDLE] Idle time: 98.61% (CPU load: 1.39%)

master:
[20012] [MEM] Free: 195016 bytes, Total: 231532 bytes, Min Free: 132460 bytes
[20012] [IDLE] Idle time: 98.53% (CPU load: 1.47%)
[30017] [MEM] Free: 195016 bytes, Total: 231532 bytes, Min Free: 132460 bytes
[30017] [IDLE] Idle time: 98.53% (CPU load: 1.47%)
[40022] [MEM] Free: 195016 bytes, Total: 231532 bytes, Min Free: 132460 bytes
[40022] [IDLE] Idle time: 98.53% (CPU load: 1.47%)
```

---

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please be transparent about their usage as it
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Did you use AI tools to help write this code? **NO**

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

* **Refactor**
* Streamlined rendering architecture by consolidating update mechanisms
across all activities, improving efficiency and consistency.
* Modernized synchronization patterns for display updates to ensure
reliable, conflict-free rendering.

* **Bug Fixes**
* Enhanced rendering stability through improved locking mechanisms and
explicit update requests.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: znelson <znelson@users.noreply.github.com>

src/activities/home/MyLibraryActivity.h

@@ -1,8 +1,4 @@
 #pragma once
-#include <freertos/FreeRTOS.h>
-#include <freertos/semphr.h>
-#include <freertos/task.h>
-
 #include <functional>
 #include <string>
 #include <vector>
@@ -13,12 +9,9 @@
 
 class MyLibraryActivity final : public Activity {
  private:
-  TaskHandle_t displayTaskHandle = nullptr;
-  SemaphoreHandle_t renderingMutex = nullptr;
   ButtonNavigator buttonNavigator;
 
   size_t selectorIndex = 0;
-  bool updateRequired = false;
 
   // Files state
   std::string basepath = "/";
@@ -28,10 +21,6 @@ class MyLibraryActivity final : public Activity {
   const std::function<void(const std::string& path)> onSelectBook;
   const std::function<void()> onGoHome;
 
-  static void taskTrampoline(void* param);
-  [[noreturn]] void displayTaskLoop();
-  void render() const;
-
   // Data loading
   void loadFiles();
   size_t findEntry(const std::string& name) const;
@@ -48,4 +37,5 @@ class MyLibraryActivity final : public Activity {
   void onEnter() override;
   void onExit() override;
   void loop() override;
+  void render(Activity::RenderLock&&) override;
 };