[Followup #249] refactor: cleanup code and unify interfaces

[kaijchen]

What changes were proposed in this pull request?

Followup #249. Cleanup code and unify interfaces.

Why are the changes needed?

Cleanup code and unify interfaces.

Does this PR introduce any user-facing change?

No.

How was this patch tested?

CI.

[codecov-commenter]

Codecov Report

Merging #558 (7e71582) into master (5cba4e7) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@             Coverage Diff              @@
##             master     #558      +/-   ##
============================================
- Coverage     60.87%   60.86%   -0.01%     
+ Complexity     1796     1793       -3     
============================================
  Files           213      213              
  Lines         12372    12371       -1     
  Branches       1050     1049       -1     
============================================
- Hits           7531     7530       -1     
  Misses         4434     4434              
  Partials        407      407              

Impacted Files	Coverage Δ
...org/apache/uniffle/server/ShuffleFlushManager.java	84.45% <100.00%> (+0.08%)	⬆️
.../org/apache/uniffle/server/ShuffleTaskManager.java	76.62% <100.00%> (-0.14%)	⬇️
...he/uniffle/server/buffer/ShuffleBufferManager.java	83.98% <100.00%> (ø)

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[kaijchen]

Thanks @advancedxy for the review.