[api] Fixes QaServingTranslator output format

[frankfliu]

Description

Brief description of what this PR is about

• If this change is a backward incompatible change, why must this change be made?
• Interesting edge cases to note here

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 68.00000% with 8 lines in your changes missing coverage. Please review.

Project coverage is 58.91%. Comparing base (b6656ed) to head (ee2ecb3).
Report is 9 commits behind head on master.

Files with missing lines	Patch %	Lines
...l/modality/nlp/translator/QaServingTranslator.java	40.00%	6 Missing ⚠️
...anslator/TokenClassificationServingTranslator.java	0.00%	1 Missing ⚠️
...rc/main/java/ai/djl/ndarray/BytesSupplierImpl.java	50.00%	1 Missing ⚠️

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Additional details and impacted files

@@              Coverage Diff              @@
##             master    #3500       +/-   ##
=============================================
- Coverage     72.52%   58.91%   -13.62%     
+ Complexity     7394     5856     -1538     
=============================================
  Files           672      674        +2     
  Lines         32909    33042      +133     
  Branches       3501     3523       +22     
=============================================
- Hits          23868    19467     -4401     
- Misses         7400    12093     +4693     
+ Partials       1641     1482      -159     

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