stress: implement tools/stress/scripts/test-teardown

[elitegreg]

Why

The doc requires the DUT be restored to its pre-study state and proven so via diff. Bundling this in a script ensures every run ends the same way.

See Notion design for full context.

Scope

Takes --working-dir, --dut-host, --run-id, --installed-agent (bool). Performs:

1. configure replace checkpoint:pre-hwstress-<run-id>.
2. show run → <wd>/running-config.post.txt; diff against running-config.pre.txt and require empty (or fully-annotated exception).
3. If --installed-agent, uninstall the agent package.
4. Remove all access-pass, user, and device records created during the run (driven by IDs in <wd>/orchestrator-runlog.json).
5. Stop the stress controller (PID from <wd>/stress-controller.json).

Acceptance

• Pre/post show run diff is empty on the standard happy path.
• Onchain user count for the alternate program returns to 0.
• DUT has no doublezero-agent process running and no /etc/doublezero config remaining (when --installed-agent was set).

Tracker: #3744.