cherry-pick #480 to release-4.0

Signed-off-by: Hillium maruruku@stu.csust.edu.cn

What problem does this PR solve?

implement #478

What is changed and how it works?

We make serval changes to make the log of time cost correct:

1. collect kv and size each time of importing.
   

   br/pkg/restore/import.go

   Lines 328 to 331 in d9d6207

   	}
   	summary.CollectSuccessUnit(summary.TotalKV, 1, file.TotalKvs)
   	summary.CollectSuccessUnit(summary.TotalBytes, 1, file.TotalBytes)
   	}

2. a log of real time cost is added to the summary.
3. collect the success unit when checksumming, so the total cost field would be (the time of restoring + the time of checksumming) instead of just the time of restoring.

Check List

Tests

• Manual test (add detailed scripts or steps below)

Release Note

• Add real time cost to log.