[tool] longest_common_prefix

[1998LJ]

Closes #415

Implementation

• Added tools/longest_common_prefix.py to extract longest common prefix of two comma-separated strings.
• Tested matching substrings, empty prefixes, and exact matches.

[abduznik]

Logic is correct but the tool only supports exactly 2 comma-separated strings — the name longest_common_prefix implies it should work on an arbitrary list of strings. Please generalize to accept any number of strings, or clarify in the description that it's 2-string only.

[abduznik]

Thanks for the contribution! Two quick items before merge:

1. Missing tests — CONTRIBUTING.md requires tests. Please add a following the existing test pattern.
2. Header format — The header comment uses 'returns' instead of the arrow format. It should be:

   # longest_common_prefix("flower,flow,flight") → "fl"

Let me know once updated!

[1998LJ]

Thanks for the review!

I have updated the PR with the requested changes:

• Corrected header comment to arrow format (# longest_common_prefix("flower,flow,flight") → "fl").
• Added multi-string support for comma-separated inputs.
• Added unit tests in tests/test_longest_common_prefix.py.
• Synced with upstream main; full test suite passes locally (180 passed).

[abduznik]

Review comment was stale — code already handles N strings. Merging.