test(sandbox-image): remove the temporary directories tests create - #752

Summary

Each temporary directory a test creates is pushed to a roots list, and a hook removes the list's directories with rmSync(…, { recursive: true, force: true }). Every hook below is afterEach, except the one noted in notify.test.ts:

• supervisor.test.ts: a new temporaryDirectory(prefix) helper registers the 10 sites (supervise-, gate-, memory-notes-, start-marker-, computerd-store-, earlyoom-, bridge-). They are removed in the existing afterEach, after the report servers are closed.
• memory-guard.test.ts: the same helper is used for memory-notes-, earlyoom- and go-. They are removed in the existing afterEach, after the guard processes are killed.
• builds.test.ts: builds- is removed in the existing afterEach, after the started pids are killed with SIGKILL.
• notify.test.ts: the module-scope build dir cloudpid-notify- is removed in afterAll, and notify-root- in afterEach.
• comparison.test.ts (comparison-), changes.test.ts (changes-), workspaces.test.ts (workspaces-), toolchains.test.ts (bootstrap-, setup-) and docker.test.ts (cloudpid-dockerd-): a new afterEach, the same as in runs.test.ts.

runs.test.ts and workspaces.ts are unchanged: the first already cleaned up, and the second creates no temporary directories.

Evidence

• Before: 239 directories left in an isolated TMPDIR after running the 9 files on main
  After: 0

Merge Danger

Door: two-way
Blast Radius: tests-only