Use interrupt-based spi for the display

This solves our "audio stutters while scrolling" problem better! Turns
out the real root cause was the polling SPI driver blocking a whole CPU
during playback.

src/drivers/display.cpp

@@ -283,7 +283,7 @@ void Display::SendTransaction(TransactionType type,
   gpio_set_level(kDisplayDr, type);
 
   // TODO(jacqueline): Handle these errors.
-  esp_err_t ret = spi_device_polling_transmit(handle_, transaction_);
+  esp_err_t ret = spi_device_transmit(handle_, transaction_);
   ESP_ERROR_CHECK(ret);
 }
 

src/tasks/tasks.cpp

@@ -114,8 +114,7 @@ auto Priority<Type::kAudioConverter>() -> UBaseType_t {
 }
 // After audio issues, UI jank is the most noticeable kind of scheduling-induced
 // slowness that the user is likely to notice or care about. Therefore we place
-// this task directly below audio in terms of priority. Note that during audio
-// playback, this priority will be downgraded.
+// this task directly below audio in terms of priority.
 template <>
 auto Priority<Type::kUi>() -> UBaseType_t {
   return 10;

src/ui/include/ui_fsm.hpp

@@ -49,8 +49,8 @@ class UiState : public tinyfsm::Fsm<UiState> {
   void react(const tinyfsm::Event& ev) {}
 
   virtual void react(const system_fsm::BatteryStateChanged&);
-  virtual void react(const audio::PlaybackStarted&);
-  virtual void react(const audio::PlaybackFinished&);
+  virtual void react(const audio::PlaybackStarted&){};
+  virtual void react(const audio::PlaybackFinished&){};
   virtual void react(const audio::PlaybackUpdate&) {}
   virtual void react(const audio::QueueUpdate&) {}
 

src/ui/ui_fsm.cpp

@@ -91,13 +91,6 @@ void UiState::react(const system_fsm::BatteryStateChanged&) {
   UpdateTopBar();
 }
 
-void UiState::react(const audio::PlaybackStarted&) {
-  vTaskPrioritySet(NULL, 0);
-}
-void UiState::react(const audio::PlaybackFinished&) {
-  vTaskPrioritySet(NULL, 10);
-}
-
 void UiState::UpdateTopBar() {
   auto battery_state = sServices->battery().State();
   bool has_queue = sServices->track_queue().GetCurrent().has_value();