PERF: use labels to find duplicates in multi-index
```
-------------------------------------------------------------------------------
Test name                                    | head[ms] | base[ms] |  ratio   |
-------------------------------------------------------------------------------
multiindex_duplicated                        | 139.2883 | 469.6666 |   0.2966 |
-------------------------------------------------------------------------------
Test name                                    | head[ms] | base[ms] |  ratio   |
-------------------------------------------------------------------------------

Ratio < 1.0 means the target commit is faster then the baseline.
Seed used: 1234

Target [2b99b80] : use labels to identify duplicates in multi-index
Base   [0fe43a6] : Merge pull request #9120 from minrk/nbviewer-link

fix an nbviewer link in tutorials
```
