internal: Introduce scalafix

[xerial]

Testing scalafix.

Due to scala2/3 compatibilities, we cannot enable some common rules, but at least scalacenter/scalafix#542 worked

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (7f40ab0) 82.60% compared to head (309e6d4) 82.60%.
Report is 5 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3328   +/-   ##
=======================================
  Coverage   82.60%   82.60%           
=======================================
  Files         355      355           
  Lines       14854    14861    +7     
  Branches     2497     2537   +40     
=======================================
+ Hits        12270    12276    +6     
- Misses       2584     2585    +1     

Files	Coverage Δ
...ame-di/src/main/scala/wvlet/airframe/Session.scala	86.95% <ø> (ø)
...rame/http/codegen/client/HttpClientGenerator.scala	100.00% <ø> (ø)
...n/scala/wvlet/airframe/http/grpc/GrpcContext.scala	100.00% <ø> (ø)
...rframe/http/grpc/internal/GrpcServiceBuilder.scala	95.45% <ø> (ø)
...n/src/main/scala/wvlet/airframe/json/package.scala	59.09% <ø> (ø)
...-rx/src/main/scala/wvlet/airframe/rx/package.scala	100.00% <ø> (ø)

... and 3 files with indirect coverage changes

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