add mupdf perf_counters

kindlecomicconverter/comic2ebook.py

@@ -794,10 +794,13 @@ def mupdf_pdf_process_pages_parallel(filename, output_dir, target_height):
     print("Starting %i processes for '%s'." % (cpu, filename))
 
     try:
+        start = perf_counter()
         with Pool() as pool:
             results = pool.map(
                 render_page if render else extract_page, vectors
             )
+        end = perf_counter()
+        print(f"MuPDF: {end - start} sec")
     except Exception as e:
         raise UserWarning(f"Error while processing PDF pages: {e}")