fetch_job() collects what check_job() reports on: the messages of a
finished batch, the report of a background research job, or the LLMMessage
of a chat from send_chat(). On a chat it waits for the reply if it has not
arrived yet.
fetch_job(.job, .provider = NULL, ...)Fetched results; type depends on .job.
A tidyllm_chat_job, a tidyllm_research_job, or a batch object
from send_batch().
A provider function; required for batch jobs and ignored by the others.
Additional arguments passed to the underlying function.