Many index-based walking of linked lists

There are many cases of walking linked lists using index iteration, which will be exponentially slower than using list iterators.

Replacing these is simple, such as replacing the slow strategy

        for (size_t target_index = 0; target_index < uint64_list_size(self->targets); target_index++)
        {
            QCBOREncode_AddUInt64(&encoder, *uint64_list_get(self->targets, target_index));
        }

with the iterator strategy

        uint64_list_it_t it;
        for (uint64_list_it(it, self->targets); !uint64_list_end_p(it); uint64_list_next(it))
        {
            QCBOREncode_AddUInt64(&encoder, *uint64_list_cref(it));
        }

Search the repository for linked-list loops using size and index-based access, then compare each case with the uint64_list iterator example in the issue. Replace the applicable walking patterns and verify that all relevant cases use iterators without breaking the project’s existing checks.