Production implementation phase T3 (~4 days). Can run in parallel with T2.
Changes:
- Production __bulk_find_rightmost_internal() — O(log N) walk from root to find the rightmost internal page
- Production __bulk_attach_rightmost_leaf() — append rightmost child, atomically publish new WT_PAGE_INDEX
Test: catch2 — single-level internal page, multi-level internal page split, root split scenarios
Depends on: WT-17212 (T1)
Can run in parallel with: T2