Map model provider names to translator functions.
The dictionary maps provider names (e.g. 'openai', 'anthropic') to another
dictionary with two keys:
'translate_content': Function to translate AIMessage content.'translate_content_chunk': Function to translate AIMessageChunk content.When calling content_blocks on an AIMessage or AIMessageChunk, if
model_provider is set in response_metadata, the corresponding translator
functions will be used to parse the content into blocks. Otherwise, best-effort parsing
in BaseMessage will be used.