update django-ninja, including pydantic v2 and add provisional level api

src/c3nav/api/schema.py

@@ -1,5 +1,15 @@
+from typing import Literal
+
 from ninja import Schema
+from pydantic import Field as APIField
 
 
 class APIErrorSchema(Schema):
     detail: str
+
+
+class PolygonSchema(Schema):
+    type: Literal["Polygon"]
+    coordinates: list[list[tuple[float, float]]] = APIField(
+        example=[[1.5, 1.5], [1.5, 2.5], [2.5, 2.5], [2.5, 2.5]]
+    )