audren: Make use of nodiscard, rework downmixing, release all buffers

Preliminary work for upmixing & general cleanup. Fixes basic issues in games such as Shovel Knight and slightly improves the LEGO games. Upmixing stitll needs to be implemented.

Audio levels in a few games will be fixed as we now use the downmix coefficients when possible instead of supplying our own

src/audio_core/audio_out.cpp

@@ -43,6 +43,10 @@ std::vector<Buffer::Tag> AudioOut::GetTagsAndReleaseBuffers(StreamPtr stream,
     return stream->GetTagsAndReleaseBuffers(max_count);
 }
 
+std::vector<Buffer::Tag> AudioOut::GetTagsAndReleaseBuffers(StreamPtr stream) {
+    return stream->GetTagsAndReleaseBuffers();
+}
+
 void AudioOut::StartStream(StreamPtr stream) {
     stream->Play();
 }