ETT-1332 My Collections won't display page 2

[moseshll]

• This bug affects all "lists of collections" (NOT "lists of collection items" i.e., items in a single collection)
• The pagination math behind how the results array is sliced, is incorrect in that it does not multiply by items per page
• Since we have a nice Data::Page object created at the end of the routine, I just move it ahead of the slicing and adjust for 0-based vs 1-based indexing.
• The Data::Page code uses a config value for items per page; the bug locale uses hardcoded 100; I swapped in the former.

Reviewer:
Compare production vs dev-2 (or your own version):

• Choose any criteria for a list of collections > 100, as a not-logged-in user the simplest way is to use the 9700-odd-member Shared Collections, https://babel.hathitrust.org/cgi/mb?a=listcs;colltype=all
• The list starts with -------2024_REFERENCES followed by 'Generations', continuing on down to the last entry 1934.
• Go to page 2 of the results: on production the page starts with 'Generations' but the dev-2 version starts with 1835 which I think we can be confident is the beginning of the correct slice.

[carylwyatt]

It's truly amazing that no one has reported this bug before now! Excellent sleuthing and fix.

I tested jumping to page 47 of results and paging my way back and forth. It all looks in order! Approve!