fix: add matplotlib dependency and print duration with early exit in plot script

- Add matplotlib to pip install in Makefile to resolve missing import
- Insert duration print and exit() call before unused json/logs processing block in plot.py

plot.py

@@ -248,7 +248,9 @@ if __name__ == "__main__":
 
                     g.write(f"**{label}**: ```{result[day]}```\n\n")
             f.write(f"**{label}**: ```{result[day]}```\n\n")
-    
+
+    print("Duration: {}".format(time.time() - time_start))
+    exit()
     import json
     for file in pathlib.Path(".").glob("logs_plain/*.txt"):
         print("Working on: {}".format(file))