When container_persistent=false, the inner mini-swe-agent cleanup only
runs 'docker stop' in the background, leaving containers in Exited state.
Now cleanup() also runs 'docker rm -f' to fully remove the container.
Also fixes pre-existing test failures in model_metadata (gpt-4.1 1M context),
setup tests (TTS provider step), and adds MockInnerDocker.cleanup().
Original fix by crazywriter1. Cherry-picked and adapted for current main.
Fixes#1679