feat(search): add whoosh-compat, the shared field table and the field registry

src/documents/tests/search/test_fields.py

@@ -0,0 +1,10 @@
+from whoosh_compat import FieldKind
+
+from documents.search._fields import PUBLIC_FIELDS
+
+
+class TestPublicFields:
+    def test_json_fields_have_subpaths(self) -> None:
+        for field in PUBLIC_FIELDS:
+            if field.kind is FieldKind.JSON:
+                assert field.subpaths, f"{field.name} is JSON but has no subpaths"