Update OAI fetcher to throw error if no records found

[amywieliczka]

@christinklez this should address the Quartex issue we were just talking about in standup

[amywieliczka]

@barbarahui this is a bit of a duplicate of your empty metadata page handling. I'm going to let that land first since it's a bit more encompassing and then update this after. OaiFetcher.check_page could return 0 instead of raising an error.

[amywieliczka]

Hey @barbarahui did you ever take a look at this? I think there's overlap in the work you did re: empty pages?

[barbarahui]

@amywieliczka This is compatible with the work I did re. empty pages. The change I made to the Fetcher in that PR was to write the vernacular page to S3 if we were able to fetch one, regardless of the number of records that check_page() finds. I also added a warning to the log if the number of records is 0, where previously we had neither a warning nor an error.

Since in this PR you raise an error in the oai_fetcher rather than Fetcher, this works just fine with what's in main for now. We should still go back at some point and do a holistic review of our approach and be consistent about how we handle pages without metadata (both at the fetching and mapping stage).