Summary:

• Add edge-case unit tests in tests/test_numbits.py for numbits.py round-tripping (empty input, single line, large line numbers, idempotency of nums_to_numbits then numbits_to_nums) and assert numbits_any_intersection on disjoint vs overlapping sets — pure mechanical test additions with no behavior change.
• Keep the change narrow so it is straightforward to review.

Notes:

• I kept this scoped to the relevant implementation and tests.