Fix python 3.10 issue, and update cursor rules with 3.10+

.cursorrules

@@ -1,3 +1,4 @@
  - Always assume pydantic 2 (not pydantic 1)
  - Always use pytest for tests
+ - The project supports Python 3.10 and above
 

libs/core/kiln_ai/adapters/prompt_builders.py

@@ -1,6 +1,6 @@
 import json
 from abc import ABCMeta, abstractmethod
-from enum import StrEnum
+from enum import Enum
 from typing import Annotated, Dict
 
 from pydantic import AfterValidator
@@ -397,7 +397,7 @@ def chain_of_thought_prompt(self) -> str | None:
 
 
 # Generators that can take any task and build a prompt
-class PromptGenerators(StrEnum):
+class PromptGenerators(str, Enum):
     SIMPLE = "simple_prompt_builder"
     MULTI_SHOT = "multi_shot_prompt_builder"
     FEW_SHOT = "few_shot_prompt_builder"