feat(executor): remove the need to have both sync and async versions of the function

[jjmachan]

Unifed the calls to LLM, embeddings and json_loader with the following logic

if is_async: # just call the async version
	return await self._asafe_load(text=text, llm=llm, callbacks=callbacks)
else: # call the sync version inside the event_loop
	loop = asyncio.get_event_loop()
	safe_load = partial(
		self._safe_load, text=text, llm=llm, callbacks=callbacks
	)
	return await loop.run_in_executor(
		None,
		safe_load,
	)

LLM

async def generate(
	self,
	prompt: PromptValue,
	n: int = 1,
	temperature: float = 1e-8,
	stop: t.Optional[t.List[str]] = None,
	callbacks: Callbacks = [],
	is_async: bool = True,
) -> LLMResult:

Embeddings

async def embed_texts(
	self, texts: List[str], is_async: bool = True
) -> t.List[t.List[float]]:

Json Load

async def safe_load(
	self,
	text: str,
	llm: BaseRagasLLM,
	callbacks: Callbacks = None,
	is_async: bool = True,
):