Fix resource leak in ExecuteQueryToFile

[Copilot]

DbDataReader from ExecuteReaderAsync() was not disposed, causing connection pool exhaustion and potential database locks under load.

Changes

• Wrapped DbDataReader in using statement in CsvFileWriter.SaveQueryToCSV

// Before
var reader = await SqlCommand.ExecuteReaderAsync(cancellationToken).ConfigureAwait(false);
output = DataReaderToCsv(reader, csvFile, Options, cancellationToken);

// After  
using (var reader = await SqlCommand.ExecuteReaderAsync(cancellationToken).ConfigureAwait(false))
{
    output = DataReaderToCsv(reader, csvFile, Options, cancellationToken);
}

No functional changes - purely resource management.

Original prompt

Analyze ExecuteQueryToFile task and see if there are some mem leak issues that can be identified

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