refactor: CursorDirection enum, cursor value parsing and __class_getitem__ caching (#144)

tests/test_crud.py

@@ -7,7 +7,7 @@ from sqlalchemy.ext.asyncio import AsyncSession
 from sqlalchemy.orm import selectinload
 
 from fastapi_toolsets.crud import CrudFactory, PaginationType
-from fastapi_toolsets.crud.factory import AsyncCrud
+from fastapi_toolsets.crud.factory import AsyncCrud, _CursorDirection
 from fastapi_toolsets.exceptions import NotFoundError
 
 from .conftest import (
@@ -2016,7 +2016,7 @@ class TestCursorPaginatePrevCursor:
         assert isinstance(page1.pagination, CursorPagination)
 
         # Manually craft a backward cursor before any existing id
-        before_all = _encode_cursor(0, direction="prev")
+        before_all = _encode_cursor(0, direction=_CursorDirection.PREV)
         empty = await IntRoleCursorCrud.cursor_paginate(
             db_session, cursor=before_all, items_per_page=5, schema=IntRoleRead
         )

tests/test_schemas.py

@@ -324,6 +324,10 @@ class TestPaginatedResponse:
         assert CursorPaginatedResponse[dict] in union_args
         assert OffsetPaginatedResponse[dict] in union_args
 
+    def test_class_getitem_is_cached(self):
+        """Repeated subscripting with the same type returns the identical cached object."""
+        assert PaginatedResponse[dict] is PaginatedResponse[dict]
+
     def test_class_getitem_with_typevar_returns_generic(self):
         """PaginatedResponse[TypeVar] falls through to Pydantic generic parametrisation."""
         from typing import TypeVar