test+types: address Copilot nits on #15318

Three minor cleanups from Copilot's review on #15318:

1. ``_parse_launchd_list_output`` return type: ``set`` → ``set[int]``
   (matches the ``seen: set[int] = set()`` style elsewhere in the
   module).
2. ``_get_service_pids`` return type + local: same parameterization;
   was bare ``set`` before this branch existed, but Copilot flagged
   the pre-existing annotation while reviewing the diff so worth
   tightening as a drive-by.
3. ``unittest.mock.patch`` was imported in
   ``test_gateway_pid_detection_macos.py`` but never called — the
   tests use ``monkeypatch`` exclusively.  Removed the unused import.

No behaviour change.  39/39 tests still pass locally.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

tests/hermes_cli/test_gateway_pid_detection_macos.py

@@ -33,7 +33,6 @@ These tests pin the fixes at the production-code entry points:
   invocation ever regresses to ``eww``.
 """
 from types import SimpleNamespace
-from unittest.mock import patch
 
 import pytest