adds vt sequence DECPS

[Utkarsh-khambra]

closes #237

• Write tests
• Support Qt6

[christianparpart]

@Utkarsh-khambra with regards to the build failures when building using Qt6 (the one CI test), the QAudioOutput API has changed slightly.

I hope it's possible to #ifdef that out to distinguish between < QT_VERSION(6, 0, 0) and >=.

Do we actually have any possibility to run Qt6 on Linux already (with what distro)? Hmm...

[Utkarsh-khambra]

Fedora has qt6 package in their repo.

[christianparpart]

Write tests

I think here the test should be sufficient if it's abstractr, not testing the actual audio but only if it's forwarded correctly to the event listener.

[christianparpart]

@Utkarsh-khambra my modifications (squashed)

diff --git a/src/contour/Audio.cpp b/src/contour/Audio.cpp
index d8050edb..01bd527d 100644
--- a/src/contour/Audio.cpp
+++ b/src/contour/Audio.cpp
@@ -42,6 +42,7 @@ Audio::Audio()
     QAudioFormat f;
     f.setSampleRate(44100);
     f.setChannelCount(1);
+
 #if QT_VERSION >= 0x060000
     f.setSampleFormat(QAudioFormat::Int16);
     QAudioDevice info(QMediaDevices::defaultAudioOutput());
@@ -51,24 +52,23 @@ Audio::Audio()
     f.setByteOrder(QAudioFormat::LittleEndian);
     f.setSampleType(QAudioFormat::SignedInt);
     QAudioDeviceInfo info(QAudioDeviceInfo::defaultOutputDevice());
-
 #endif
+
     if (!info.isFormatSupported(f))
     {
         errorlog()("Default output device doesn't support 16 Bit signed integer PCM");
         return;
     }
-#if QT_VERSION >= 0x060000
-    audio = std::make_unique<QAudioSink>(f);
-#else
-    audio = std::make_unique<QAudioOutput>(f);
+
+#if QT_VERSION < 0x060000
+    using QAudioSink = QAudioOutput;
 #endif
+
+    audio = std::make_unique<QAudioSink>(f);
+
     audio->moveToThread(&soundThread_);
-#if QT_VERSION >= 0x060000
+
     connect(audio.get(), &QAudioSink::stateChanged, this, &Audio::handleStateChanged);
-#else
-    connect(audio.get(), &QAudioOutput::stateChanged, this, &Audio::handleStateChanged);
-#endif
     qRegisterMetaType<std::vector<int>>();
     connect(this, &Audio::play, this, &Audio::handlePlayback);
     soundThread_.start();
@@ -80,17 +80,18 @@ Audio::~Audio()
     soundThread_.wait();
 }
 
-void Audio::fillBuffer(int volume, int duration, crispy::span<const int> notes)
+void Audio::fillBuffer(int volume, int duration, crispy::span<int const> notes)
 {
-    for (auto i: notes)
+    for (auto const i: notes)
     {
         auto b = createMusicalNote(volume, duration, i);
-        byteArray_.append(reinterpret_cast<const char*>(b.data()), static_cast<int>(2 * b.size()));
+        byteArray_.append(reinterpret_cast<char const*>(b.data()), static_cast<int>(2 * b.size()));
     }
 }
 
 void Audio::handlePlayback(int volume, int duration, std::vector<int> const& notes)
 {
+    Require(audio);
     if (audio->state() == QAudio::State::ActiveState)
     {
         fillBuffer(volume, duration, crispy::span(notes.data(), notes.size()));
@@ -99,8 +100,7 @@ void Audio::handlePlayback(int volume, int duration, std::vector<int> const& not
     fillBuffer(volume, duration, crispy::span(notes.data(), notes.size()));
     audioBuffer_.setBuffer(&byteArray_);
     audioBuffer_.open(QIODevice::ReadWrite);
-    if (audio)
-        audio->start(&audioBuffer_);
+    audio->start(&audioBuffer_);
 }
 
 void Audio::handleStateChanged(QAudio::State state)