Consider stopping containers with `kill`

[io7m]

Currently, the supervisor uses podman stop to stop containers. This means that they (rarely) survive the close attempt. The supervisor should give them no choice and use podman kill to destroy the processes.

This sometimes results in:

java.io.IOException: Container process Process[pid=3558105, exitValue="not exited"] is still alive!

	at com.io7m.ervilla.native_exec@0.0.5/com.io7m.ervilla.native_exec.internal.EContainerSupervisor$EContainer.stop(EContainerSupervisor.java:919)
	at com.io7m.northpike.tests@0.0.1-SNAPSHOT/com.io7m.northpike.tests.containers.NPTestContainers$NPIdstoreFixture.reset(NPTestContainers.java:269)
	at com.io7m.northpike.tests@0.0.1-SNAPSHOT/com.io7m.northpike.tests.user_client.NPUserClientTest.setup(NPUserClientTest.java:142)
	at java.base/java.lang.reflect.Method.invoke(Method.java:568)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1511)