Follow-up to the salvaged #43846 commits: the WhatsApp adapter moved from
gateway/platforms/whatsapp.py to plugins/platforms/whatsapp/adapter.py since the
PR was authored. The cherry-pick brought _listener_pids_on_port's `re.finditer`
ss-fallback and the new test's import, but the new module location doesn't import
`re` (latent NameError on the lsof-absent fallback path) and the test imported the
old module path. Add `import re` to the adapter and repoint the test import.
615a8e6516