AnalyzerTrack: Make constructor explicit

To prevent accidentally passing just the track and thereby discarding
option overrides.

See mixxxdj#11872 (comment)

src/analyzer/analyzertrack.h

@@ -12,7 +12,7 @@ class AnalyzerTrack {
         std::optional<bool> useFixedTempo;
     };
 
-    AnalyzerTrack(TrackPointer track, Options options = Options());
+    explicit AnalyzerTrack(TrackPointer track, Options options = Options());
 
     /// Fetches the (not-null) track to be analyzed.
     const TrackPointer& getTrack() const;