feat: Custom errors fallback

[yoschihirokaimoto]

[CaiqueMitsuoka]

Hey @brainlid thanks for the review. This open by mistake, it suppose to be opened to our fork haha. I'm glad you liked, we are testing this in our app. The ideia is give control to tools so they can stop the chain and preserve the state. On some tools we have specific responses that we want to send instead of having the LLM process the rest. But it can be used to guardrails, abort, etc... Lets make a good version of it with tests and docs and have make the contribution 💪