[feature](function) Support levenshtein distance function

[kzh1458003655-web]

What problem does this PR solve?

Implemented the Levenshtein Distance function for string comparison.

Syntax: levenshtein(str1, str2)

Return: Returns the Levenshtein distance (int32) between two strings.

Tests

Added comprehensive unit tests in be/test/vec/function/function_levenshtein_test.cpp. Verified with various cases including empty strings, basic edits, and unicode characters.

[hello-stephen]

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1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
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