Optimize account hash CumulativeOffset index from vec to 2-element array

[HaoranYi]

Problem

Optimize CumulativeOffset for raw data index during accounts hash calculation.

The raw data is at most 2d. Therefore, instead of using a Vec to store one or two indexes to the data, we can change it to use [usize; 2].

This saves heap allocation and one pointer deref when reading the index.

Summary of Changes

Use [usize; 2] for CumulativeOffset

Fixes #

[codecov]

Codecov Report

Merging #33839 (73910a7) into master (6470544) will increase coverage by 0.0%.
The diff coverage is 100.0%.

❗ Current head 73910a7 differs from pull request most recent head 911c9d9. Consider uploading reports for the commit 911c9d9 to get more accurate results

@@           Coverage Diff           @@
##           master   #33839   +/-   ##
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  Coverage    81.8%    81.9%           
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  Files         809      809           
  Lines      217712   217712           
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+ Hits       178295   178309   +14     
+ Misses      39417    39403   -14     

[brooksprumo]

Nice observation!

[jeffwashington]

looks like a good idea!