- uppercase ISBN before checking it's a number to account for trailing 'x'
- check maybe_isbn for search_identifiers search. Without this we are only searching external connectors, not locally!
ISBNs are always numeric except for when the check digit in ISBN-10s is a ten, indicated with a capital X.
These changes ensure that ISBNs are always upper-case so that a lower-case 'x' is not used when searching.
Additionally some ancient ISBNs have been printed without a leading zero (i.e. they only have 9 characters on the physical book). This change prepends a zero if something looks like an ISBN but only has 9 chars.
Since we get all the results quickly now, this aggregates all the
results that came back and sorts them by confidence, and returns the
highest confidence result. The confidences aren't great on free text
search, but conceptually that's how it should work at least.
It may make sense to aggregate the search results in all contexts, but
I'll propose that in a separate PR.