Upgrade bootstrap module

Replace `bootstrap.n_random_resamples` with [`verify.iterative_blocked_bootstrap`](https://github.com/dougiesquire/Squire_2022_CAFE-f6/blob/main/src/verify.py). The new code is completely lazy, substantially faster and does "nested" bootstrapping, which `n_random_resamples` doesn't.

Inspect the repository’s uses of `bootstrap.n_random_resamples`, then compare them with `iterative_blocked_bootstrap` in the linked `src/verify.py`. Replace the old bootstrap path while preserving the surrounding behavior, and verify that the resulting analysis uses the lazy, nested bootstrap implementation described in the issue.

Written by the indexing model from the issue text.