Allow option to keep the containers alive

It would be nice to keep the docker containers alive for speeding up the test runs. Now, in every test run containers are re-created and can't keep them alive since this block

  def __del__(self):
        """
        Try to remove the container in all circumstances
        """
        if self._container is not None:
            try:
                self.stop()
            except:  # noqa: E722
                pass

removes containers when the instance variable is deleted (when the program terminates) and I cannot override it because this also runs without using with as block.

I don't want my Mysql container to be recreated everytime. I am running tests very frequently and I am waiting couple seconds everytime. Pretty annoying.

I can make a small PR if that makes sense?

Start by reading testcontainers/core/container.py around the del method and trace how containers are stopped when a test run ends, including use outside a with block. Define the option's lifecycle behavior for both context-managed and directly created containers; done means a caller can keep a MySQL container alive across runs without automatic cleanup.