### Summary
Adopt sync.WaitGroup.Go (Go 1.25) to simplify tracked goroutine
spawning. This replaces the error-prone trio of wg.Add(1), go func(),
and defer wg.Done() with a single, self-contained call.
More info: https://github.com/golang/go/issues/63796
Signed-off-by: grandpig <grandpig@outlook.com>
### What problem does this PR solve?
Package refactor and PDF post process.
### Type of change
- [x] Refactoring
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Co-authored-by: Claude <noreply@anthropic.com>