This commit introduces concurrency to the AI digest generation to improve performance.
The `BuildDigestDataByAI` function now processes each primary group in a separate goroutine.
A `sync.WaitGroup` is used to wait for all goroutines to complete.
A `sync.Mutex` is used to protect concurrent access to the results slice.
The final slice of primary groups is sorted alphabetically to ensure deterministic output for testing.
eleith