Output: Add render progress logging

src/optics.h

@@ -31,6 +31,7 @@ LinearRgb blackbody_to_linear_rgb(double temperature_K);
 int psf_kernel_cache_init(PsfKernelCache *cache,
                           const PointSpreadFunction *psf);
 void psf_kernel_cache_destroy(PsfKernelCache *cache);
+void psf_kernel_cache_report_ready(const PsfKernelCache *cache, FILE *stream);
 void psf_kernel_cache_report(const PsfKernelCache *cache,
                              const PsfSplatStats *stats, FILE *stream);
 /* Reference implementation: pixel-area-integrated Moffat with the same tail