[client-v2] Handle new error tag from ClickHouse

## Description

Handle new error format from ClickHouse

Start by locating the client-v2 error-handling entry point and reviewing how the current ClickHouse error format is parsed. Confirm the new error tag and its expected behavior from the client or ClickHouse context, then add coverage for the new format and verify existing error handling still passes.

索引モデルが issue の本文から書いたものです。