0.3.19 upate

• 0.3.19 released
  • Add TotLogStream (src/casevo/util/tot_log_stream.py).
    • Since it uses the simple open(fila, 'a') method, the log directory needs to be cleared when running it again.
    • The output format has been changed from the previous JSON to TXT.
    • Previously, it was in an array format. Now, each line in the log corresponds to an item in the previous log array, and other formats remain unchanged.
  • Add VariableNetwork in model_base.py
  • Add ToolStep for the tool calling in chain.py
  • Add CoT feature for memory reflection in momory.py.