feat: consider how we want handle new AI `.xlsx` banks data format

[jdhoffa]

Starting with the 2023Q4 release, both EO and FC for banks come in one xlsx file. adjust expectations accordingly.

cc @jacobvjk

Relates to RMI-PACTA/pacta.multi.loanbook#16

AB#10852

[cjyetman]

If we do a new release of r2dii.data along with the other r2dii.* packages in Q12025 (which I believe is not technically necessary), this may be a priority issue
@jdhoffa @jacobvjk