fix(operator): enhance connection handling in QueryHandler

[AxiosLeo]

… both callback and promise-based MySQL connection pools

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Note

Updates beginTransaction to detect mysql2 pool type and acquire a connection appropriately, converting to promise-based when needed.

• Operator (src/operator.js):
  • Transaction handling (QueryHandler.beginTransaction):
    • Detects pool type (Pool vs PromisePool) via promise() presence.
    • For callback pools: wraps getConnection in a Promise and converts connection with conn.promise().
    • For promise pools: directly awaits getConnection().
    • Retains pool-connection release on commit/rollback.

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