Morebuiltins

1. add `cmd.log_server`
2. add start_callback end_callback to `ipc.SocketServer`
1. ipc: self.handler(self, item) -> self.handler(item)
3. add `RotatingFileWriter.flush`, and default flush=False
4. fix `StreamWriter.__del__` fails if event loop is already closed

1. fix default_dict type-hint
2. fix read num zero div
3. add build_opener_handlers+proxy to request.req

1. add `utils.PathLock`

1. add `functools.file_import`

1. fix `utils.Validator` typing-hint class