bug fix for hash-based and path-based trie demo code

[ping-ke]

Changes:

1. Updates get_nbit to traverse key bits in ascending order (0 → 255) for hash.py & path.py.
2. Updates test cases so that input keys are consistent with the corrected get_nbit behavior and expected tree evolution.
3. Modify boundary bug in loops.
4. Update expected behavior for path.py.