Rename `.extract_data()` and `.extract_data_async()`

[gadenbuie]

ellmer v0.2.0 renamed extract_data() to chat_structured(). The new name matches the patterns for batch_chat_structured() and parallel_chat_structured() and is a bit more clear in its purpose (extract_data() sounds like something you'd call to pull data out of a response rather than to ask the LLM to provided a structured response).

tidyverse/ellmer#481

[cpsievert]

Done in #175