Exception Handling Policy

[BenConstable9]

Why are these changes needed?

This adds an exception handling policy that allows the group chat to raise the underlying exception if needed. Default behaviour is not changed.

Related issue number

Closes #4904

Checks

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• I've added tests (if relevant) corresponding to the changes introduced in this PR.
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[ekzhu]

@jackgerrits @BenConstable9 for AgentChat layer, I think we should first expose the runtime as a separate parameter in the group chats' constructors, then setting the exception handling policy through the runtime's constructor.

Let's focus on the Core API layer for now?

For the AgentChat layer, if you want to set the policy, do it for now by setting the exception handling policy of the _runtime attribute directly. I believe we need to first expose runtime as a new constructor argument for the group chat classes. The correct way should be setting the policy on the runtime, and then pass the runtime through the group chats.

[jackgerrits]

Agreed with @ekzhu, let's not expose directly in agentchat for now and stick to just core. Digging up the _runtime property is a good short term compromise