cache: use render job times to synchronize cache

Ensure old inaccurate jobs are never prioritized over current jobs.

app/task/render/render.h

@@ -63,6 +63,11 @@ protected:
 
   void SetAnchorPoint(const rational& r);
 
+  const qint64& job_time() const
+  {
+    return job_time_;
+  }
+
 private:
   ViewerOutput* viewer_;
 
@@ -74,6 +79,8 @@ private:
 
   OpenGLBackend backend_;
 
+  qint64 job_time_;
+
 };
 
 OLIVE_NAMESPACE_EXIT