read relationships file only once, less batches for rollover-test (#1096)
read relationships file only once, less batches for rollover-test (#1096)

> Related #https://github.com/threatgrid/iroh/issues/4920

This PR optimizes a little bit `ctia.task.migration.store-test` ns test by reading only once the relationships file samples. It also reduces the number of random batch size to test rollover-test. Not the win of year, but still useful :-)

_reviewers: hide white space changes._

build time observed [here](https://github.com/threatgrid/ctia/pull/1079/checks?check_run_id=2098372414): 
[ctia.task.migration.store-test {:elapsed-ns 235972437954}]
[ctia.task.migration.store-test/rollover-test {:elapsed-ns 6.3143038789E10}]
[ctia.task.migration.store-test/sliced-queries-test {:elapsed-ns 1.1595586681E10}]

This PR build (at time of writing):
[ctia.task.migration.store-test {:elapsed-ns 227022970930}]
[ctia.task.migration.store-test/rollover-test {:elapsed-ns 4.3493366775E10}]
[ctia.task.migration.store-test/sliced-queries-test {:elapsed-ns 1.20827999E10}]
threatgrid/ctia,threatgrid/ctia,saintx/ctia,saintx/ctia,yogsototh/ctia,saintx/ctia,threatgrid/ctia,yogsototh/ctia,threatgrid/ctia,yogsototh/ctia