Get the text content of the message as a string.
Can be used as both property (message.text) and method (message.text()).
Handles both string and list content types (e.g. for content blocks). Only
extracts blocks with type: 'text'; other block types are ignored.
As of langchain-core 1.0.0, calling .text() as a method is deprecated.
Use .text as a property instead. This method will be removed in 2.0.0.
text: TextAccessor