fix: sift categories endpoint to not use drf

api/book/serializers.py

-from rest_framework import serializers
-
-from book.models import Book, Category
-
-
-class CategorySerializer(serializers.ModelSerializer):
-    class Meta:
-        model = Category
-        fields = "__all__"
-
-
-class BookSerializer(serializers.ModelSerializer):
-    category_detail = CategorySerializer(source="category", read_only=True)
-
-    class Meta:
-        model = Book
-        fields = "__all__"