Annotate list link attrs with Sequence type

This is beneficial as lists are invariant and we're using a union type
here with User | Link[User], which means we can't assign a list[User] to
the attr, which is very annoying.

src/api/categories.py

@@ -160,7 +160,9 @@ async def delete_category(category_id: PydanticObjectId, user: CurrentUserDep) -
     # and it's far more sensible solution than deleting all events with this category)
     events = await Event.find(category in Event.categories).to_list()
     for event in events:
-        event.categories.remove(category)
+        new_categories = list(event.categories)
+        new_categories.remove(category)
+        event.categories = new_categories
     await Event.replace_many(events)
 
     # We can now safely delete the category

src/db/models/event.py

@@ -1,3 +1,4 @@
+from collections.abc import Sequence
 from datetime import UTC, date, datetime, time
 from typing import Annotated, ClassVar, final
 
@@ -15,13 +16,13 @@ class Event(Document):
     user: Annotated[User, Annotated[Link[User], Indexed()]]
     title: str
     description: str
-    categories: Annotated[list[Category | Link[Category]], Annotated[list[Link[Category]], Indexed()]]
+    categories: Annotated[Sequence[Category | Link[Category]], Annotated[list[Link[Category]], Indexed()]]
     start_date: Annotated[date, Indexed()]
     start_time: time
     end_date: Annotated[date, Indexed()]
     end_time: time
     color: str  # TODO: Consider using a complex rgb type
-    attendees: Annotated[list[User | Link[User]], Annotated[list[Link[User]], Indexed()]]
+    attendees: Annotated[Sequence[User | Link[User]], Annotated[list[Link[User]], Indexed()]]
     created_at: datetime = Field(default_factory=lambda: datetime.now(UTC))
 
     @final