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/circuits/models/circuits.py

@@ -8,10 +8,16 @@ from django.utils.translation import gettext_lazy as _
 from circuits.choices import *
 from dcim.models import CabledObjectModel
 from netbox.models import ChangeLoggedModel, OrganizationalModel, PrimaryModel
-from netbox.models.mixins import DistanceMixin
 from netbox.models.features import (
-    ContactsMixin, CustomFieldsMixin, CustomLinksMixin, ExportTemplatesMixin, ImageAttachmentsMixin, TagsMixin,
+    ContactsMixin,
+    CustomFieldsMixin,
+    CustomLinksMixin,
+    ExportTemplatesMixin,
+    ImageAttachmentsMixin,
+    TagsMixin,
 )
+from netbox.models.mixins import DistanceMixin
+
 from .base import BaseCircuitType
 
 __all__ = (

netbox/circuits/models/virtual_circuits.py

@@ -9,6 +9,7 @@ from django.utils.translation import gettext_lazy as _
 from circuits.choices import *
 from netbox.models import ChangeLoggedModel, PrimaryModel
 from netbox.models.features import CustomFieldsMixin, CustomLinksMixin, ExportTemplatesMixin, TagsMixin
+
 from .base import BaseCircuitType
 
 __all__ = (