Fixes the inconsistent usage of msgpack/json in graph reporter

[sighingnow]

Related issue number

Fixes #2823.

[codecov-commenter]

Codecov Report

Merging #2843 (1e423ee) into main (1ba6102) will increase coverage by 0.14%.
The diff coverage is 88.88%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2843      +/-   ##
==========================================
+ Coverage   42.44%   42.59%   +0.14%     
==========================================
  Files          99       99              
  Lines       10654    10657       +3     
==========================================
+ Hits         4522     4539      +17     
+ Misses       6132     6118      -14     

Impacted Files	Coverage Δ
python/graphscope/client/session.py	66.77% <66.66%> (+0.16%)	⬆️
python/graphscope/framework/app.py	70.77% <100.00%> (+0.91%)	⬆️
python/graphscope/framework/context.py	45.19% <100.00%> (+0.56%)	⬆️
python/graphscope/framework/graph.py	69.71% <100.00%> (ø)

... and 4 files with indirect coverage changes

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[siyuan0322]