refactor: Simplify isReaderActivity bookkeeping (#1838)

## Summary

Before, any sub-activity of a reader activity needed to override
`isReaderActivity` to maintain correct bookkeeping through
`ActivityManager::isReaderActivity`. We could easily miss this in any
new sub-activities. Instead, simplify so each reader activity correctly
reports and then `ActivityManager` checks for any reader activity in its
stack.

---

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src/activities/ActivityManager.cpp

@@ -2,6 +2,8 @@
 
 #include <HalPowerManager.h>
 
+#include <algorithm>
+
 #include "OpdsServerStore.h"
 #include "boot_sleep/BootActivity.h"
 #include "boot_sleep/SleepActivity.h"
@@ -230,7 +232,11 @@ void ActivityManager::popActivity() {
 
 bool ActivityManager::preventAutoSleep() const { return currentActivity && currentActivity->preventAutoSleep(); }
 
-bool ActivityManager::isReaderActivity() const { return currentActivity && currentActivity->isReaderActivity(); }
+bool ActivityManager::isReaderActivity() const {
+  return std::any_of(stackActivities.begin(), stackActivities.end(),
+                     [](const auto& activity) { return activity->isReaderActivity(); }) ||
+         (currentActivity && currentActivity->isReaderActivity());
+}
 
 bool ActivityManager::skipLoopDelay() const { return currentActivity && currentActivity->skipLoopDelay(); }
 

src/activities/reader/EpubReaderChapterSelectionActivity.h

@@ -32,5 +32,4 @@ class EpubReaderChapterSelectionActivity final : public Activity {
   void onExit() override;
   void loop() override;
   void render(RenderLock&&) override;
-  bool isReaderActivity() const override { return true; }
 };

src/activities/reader/EpubReaderFootnotesActivity.h

@@ -19,7 +19,6 @@ class EpubReaderFootnotesActivity final : public Activity {
   void onExit() override;
   void loop() override;
   void render(RenderLock&&) override;
-  bool isReaderActivity() const override { return true; }
 
  private:
   const std::vector<FootnoteEntry>& footnotes;

src/activities/reader/EpubReaderMenuActivity.h

@@ -32,7 +32,6 @@ class EpubReaderMenuActivity final : public Activity {
   void onExit() override;
   void loop() override;
   void render(RenderLock&&) override;
-  bool isReaderActivity() const override { return true; }
 
  private:
   struct MenuItem {

src/activities/reader/EpubReaderPercentSelectionActivity.h

@@ -15,7 +15,6 @@ class EpubReaderPercentSelectionActivity final : public Activity {
   void onExit() override;
   void loop() override;
   void render(RenderLock&&) override;
-  bool isReaderActivity() const override { return true; }
 
  private:
   // Current percent value (0-100) shown on the slider.

src/activities/reader/KOReaderSyncActivity.h

@@ -41,7 +41,6 @@ class KOReaderSyncActivity final : public Activity {
   void loop() override;
   void render(RenderLock&&) override;
   bool preventAutoSleep() override { return state == CONNECTING || state == SYNCING; }
-  bool isReaderActivity() const override { return true; }
 
  private:
   enum State {

src/activities/reader/QrDisplayActivity.h

@@ -14,7 +14,6 @@ class QrDisplayActivity final : public Activity {
   void onExit() override;
   void loop() override;
   void render(RenderLock&&) override;
-  bool isReaderActivity() const override { return true; }
 
  private:
   std::string textPayload;

src/activities/reader/XtcReaderChapterSelectionActivity.h

@@ -23,5 +23,4 @@ class XtcReaderChapterSelectionActivity final : public Activity {
   void onExit() override;
   void loop() override;
   void render(RenderLock&&) override;
-  bool isReaderActivity() const override { return true; }
 };