use DeltaReader directly to implement Dictionnary::term_ord

[trinity-1686a]

fix #1853

[codecov-commenter]

Codecov Report

Merging #1925 (203b260) into main (ed5a3b3) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##             main    #1925      +/-   ##
==========================================
- Coverage   94.46%   94.46%   -0.01%     
==========================================
  Files         309      309              
  Lines       56485    56513      +28     
==========================================
+ Hits        53361    53387      +26     
- Misses       3124     3126       +2     

Impacted Files	Coverage Δ
sstable/src/dictionary.rs	87.74% <100.00%> (+0.73%)	⬆️
src/indexer/segment_serializer.rs	98.46% <0.00%> (-1.54%)	⬇️

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