This commit introduces the following changes:
- **BaseAgent:** Added a mechanism to allow consumers to update the AgentContext after post-processing a split. This provides more flexibility for downstream components to react to the processed data.
- **TextAgentResponseHandler:** Introduced a `beforeStream` consumer that allows updating the AgentContext before the stream begins. This enables pre-processing or initialization steps within the response handler. The constructor has been updated to accept this new consumer. Also fixed a bug where the chunkKey and updateKey were not being removed after processing.
These changes enhance the extensibility and configurability of the agent processing pipeline.
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