free of buf array in local_result_v2 struct

[agoncear-mwb]

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• Bug Fix (user-visible misbehavior in an official stable release)

Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

in the free_result_v2 func, the const char* buf field is not freed, and this can lead to memory leak.

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• Documentation is written (mandatory for new features)

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[auxten]

actually, local_result_v2._vec and local_result_v2.buf are the same memory.
See: https://github.com/chdb-io/chdb/blob/main/programs/local/LocalServer.cpp#L1261