test: add pagination bounds tests for report entries

[LeandroPG19]

Extracts the pagination math from get_searched_entries into a testable paginate<T>() helper and adds 8 tests covering all edge cases.

Before: get_report_entries.rs had zero tests. The pagination formula relied on saturating_sub and unwrap_or_default with no safety net.

After: paginate() is a generic function that takes a slice and a page number, returns the page items + total count. 8 tests cover:

Test	Scenario	Expected
test_paginate_first_page_full	75 results, page 1	30 items
test_paginate_last_page_partial	75 results, page 3	15 items
test_paginate_page_zero	page 0	empty
test_paginate_beyond_last_page	30 results, page 100	empty
test_paginate_empty_data	empty input	empty
test_paginate_exact_multiple	60 results, page 2	30 items
test_paginate_single_element	1 result, page 1	1 item
test_paginate_page_past_end_with_partial_last	45 results, page 3	empty

test result: ok. 179 passed; 0 failed
``