fix(scan): improve resource management in scanIterator

[pranavkonde]

Improve Resource Management in scanIterator

Problem

• Potential resource leaks when context is cancelled during operation
• Race conditions possible due to unordered channel closing
• Inadequate error propagation from worker goroutines

Solution

• Added error channel for proper worker error handling
• Implemented ordered cleanup sequence in Close() method
• Enhanced context cancellation handling
• Improved worker synchronization

Changes

type scanIterator struct {
    // ... existing fields ...
    errChan   chan error    // New error channel
}

func (s *scanIterator) Close() error {
    s.closeOnce.Do(func() {
        if s.cancel != nil {
            s.cancel()
        }
        s.doneWG.Wait()
        close(s.errChan)
        close(s.resultChan)
    })
    return nil
}

Testing

• Verified with context cancellation scenarios
• Tested concurrent operation cases
• Checked error propagation paths

Checklist

• Code follows project guidelines
• Changes are focused and atomic
• Manually tested