* implement serialization for chat messages and add tests
* implement serialization for ChatPromptBuilder and test it
* add reno
* solve mypy type error
* solve mypy type error
* remove flattening parameter in to_dict
* simplify to jus non-flat metadata
* try to fix linting issue
* solve format issues
* update test for ChatPromptBuilder
* remove unused import
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Co-authored-by: David S. Batista <dsbatista@gmail.com>
