Fix data export logic to avoid redundant high frequency query

[LJW21-02]

Major Changes

• Fixed SQL file export logic to avoid redundant queries during high-frequency operations

[Copilot]

Pull request overview

This pull request refactors the SQL file export logic in IoTDB to eliminate redundant high-frequency queries that were executed during data export operations. The original implementation performed a SHOW TIMESERIES query for every single data point, which caused severe performance issues.

Changes:

• Split the exportToSqlFile method into two specialized methods: exportToSqlFileWithAlignDevice for align-by-device queries and exportToSqlFileWithoutAlign for regular queries
• Removed the redundant SHOW TIMESERIES query that was executed for each row in the original implementation
• Simplified the file writing logic to use prepared SQL prefixes and avoid nested loops

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