Optimize chunked preprocessing

[Sichao25]

Optimize the speed of Preprocessor when chunked preprocessing is not enabled.

[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 26.66667% with 44 lines in your changes missing coverage. Please review.

Project coverage is 43.42%. Comparing base (117ceb5) to head (6d1262c).

Files	Patch %	Lines
dynamo/preprocessing/normalization.py	27.90%	31 Missing ⚠️
dynamo/preprocessing/gene_selection.py	20.00%	12 Missing ⚠️
dynamo/configuration.py	50.00%	1 Missing ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #674      +/-   ##
==========================================
- Coverage   43.60%   43.42%   -0.18%     
==========================================
  Files         161      161              
  Lines       28724    28748      +24     
==========================================
- Hits        12524    12485      -39     
- Misses      16200    16263      +63     

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