Fixes #21407: Enable I (isort) and stabilize import ordering (#21458)

- Adopt Ruff `I` (isort) rules for consistent import sorting
- Add two `# isort: split` boundaries to keep required imports pinned
  in `__init__.py` modules

netbox/virtualization/apps.py

@@ -7,6 +7,7 @@ class VirtualizationConfig(AppConfig):
     def ready(self):
         from netbox.models.features import register_models
         from utilities.counters import connect_counters
+
         from . import search, signals  # noqa: F401
         from .models import VirtualMachine