fix: wrap IoT-only imports in use_iot conditional to fix ruff F401/I001

MagicMock and Generator are only used in IoT fixtures. With standard
defaults (use_iot=false) they were unconditionally imported, triggering
ruff F401 (unused import) and I001 (import sort order).

Co-Authored-By: Claude <noreply@anthropic.com>

Author: namitdeb739