[CELEBORN-1565] Introduce warn-unused-import in Scala

[cxzl25]

What changes were proposed in this pull request?

This PR aims to introduce warn-unused-import in Scala.

Why are the changes needed?

There are currently many invalid imports, which can be checked using -Ywarn-unused-import. And through silencer plugin we can avoid some imports required in scala 2.11.

import org.apache.celeborn.common.util.FunctionConverter._

Does this PR introduce any user-facing change?

No

How was this patch tested?

GA

[FMX]

Finally, there is a PR to fix this problem. BTW Are there any tools to find unused methods?

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 33.24%. Comparing base (ea6617c) to head (d5686f8). Report is 52 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #2689 +/- ## ========================================== - Coverage 39.83% 33.24% -6.59% ========================================== Files 239 313 +74 Lines 15026 18275 +3249 Branches 1362 1678 +316 ========================================== + Hits 5984 6073 +89 - Misses 8711 11863 +3152 - Partials 331 339 +8 ```

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[cxzl25]

Are there any tools to find unused methods

Maybe scalafix.

https://scalacenter.github.io/scalafix/docs/rules/RemoveUnused.html

[FMX]

Please fix the conflicts. This PR looks good to me.

[FMX]

Are there any tools to find unused methods

Maybe scalafix.

https://scalacenter.github.io/scalafix/docs/rules/RemoveUnused.html

Is there any relative tools for Java?

[FMX]

Are there any tools to find unused methods

Maybe scalafix.

https://scalacenter.github.io/scalafix/docs/rules/RemoveUnused.html

Are there any relative tools for Java?

[FMX]

Are there any tools to find unused methods

Maybe scalafix.

https://scalacenter.github.io/scalafix/docs/rules/RemoveUnused.html

Are there any relative tools for Java?

[mridulm]

Isnt there not a checkstyle rule for this ?

[mridulm]

And I just realized we dont have checkstyle for Celeborn :-) Perhaps that might help with this as well as other style enforcements ?

[cxzl25]

we dont have checkstyle for Celeborn

Because we use spotless-maven-plugin, there may be some check conflicts with checkstyle. In addition, .scalafmt.conf is used in scala to check some formats.

[cxzl25]

Thanks. Merged into main(v0.6.0).