Fix node_16::grow() missing 128 offset in node_48 index population

[Copilot]

node_16::grow() populates node_48::indexes_[] without the required 128 offset, causing child lookups to fail after growth. All other node_48 operations use indexes_[128 + partial_key] for consistent byte-to-index mapping.

Changes

• include/art/node_16.hpp: Add 128 offset when populating node_48::indexes_[] during growth

  // Before
  new_node->indexes_[(uint8_t) this->keys_[i]] = i;
  
  // After
  new_node->indexes_[128 + (uint8_t) this->keys_[i]] = i;

• test/node_16.cpp: Add test case that grows node_16 to node_48 and verifies child accessibility and iterator navigation

Impact

Without this fix:

• Children inserted before growth become unreachable
• Iterator navigation returns incorrect keys
• Data effectively corrupted after any node_16→node_48 transition

Related to PR #20.

Original prompt

write a test case that reproduces the issue mentioned in #20 . The potential bug might have been fixed in the meantime. If the issue still exists, see if the provided fix solves the problem

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[Copilot]

Pull request overview

This PR fixes a critical bug in node_16::grow() where the transition from node_16 to node_48 failed to apply the required 128 offset when populating the indexes_[] array, causing child lookups and iterator navigation to fail after growth. The fix ensures consistency with all other node_48 operations which universally use indexes_[128 + partial_key] for signed-to-unsigned byte mapping.

• Add 128 offset in node_16::grow() when populating node_48 indexes_[] array
• Add comprehensive test case that verifies child accessibility and iterator navigation after node_16→node_48 growth
• Update .gitignore to exclude CodeQL metadata file

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated no comments.

File	Description
include/art/node_16.hpp	Fixed index population in grow() by adding 128 offset: indexes_[128 + (uint8_t) this->keys_[i]] instead of indexes_[(uint8_t) this->keys_[i]]
test/node_16.cpp	Added test case that grows node_16 to node_48 with 17 children and verifies find_child(), next_partial_key(), and prev_partial_key() operations work correctly
.gitignore	Added _codeql_detected_source_root to ignore CodeQL metadata

[rafaelkallis]

@copilot you should co-author bowling233 <zhubaolin228@gmail.com> as we are using parts of his contribution from #20 in this commit

[Copilot]

@copilot you should co-author bowling233 <zhubaolin228@gmail.com> as we are using parts of his contribution from #20 in this commit

I cannot amend the existing commits to add bowling233's co-authorship because force push is not available in this environment. The commits have already been pushed to the remote branch.

However, I can acknowledge bowling233's contribution in a few ways:

1. Add a commit with a message that credits bowling233 for the original fix from PR bugfix: 'node_16<T>::grow()' partial_key index offset inconsistent #20
2. Update any documentation or comments in the code to reference bowling233's work

Would you like me to add a commit message that properly credits bowling233, or would you prefer to handle the commit history update manually?