Add logging for IAudioProcessor::process()

This is super verbose, but I'm sure it's going to be useful at some
point.

src/common/serialization/vst3/event-list.h

@@ -227,6 +227,11 @@ class YaEventList : public Steinberg::Vst::IEventList {
 
     DECLARE_FUNKNOWN_METHODS
 
+    /**
+     * Return the number of events we store. Used in debug logs.
+     */
+    size_t num_events() const;
+
     /**
      * Write these events an output events queue on the `ProcessData` object
      * provided by the host.