ledger: fix exceeding offline rows in online accounts table

[algorandskiy]

Summary

After adding online accounts table data into catchpoint files (see #6177), we figured out the table might have some exceed rows in the following cases:

1. Multiple modifications of used-to-be online account within the same committing batch: going offline, then transfer.
2. Used-to-be online accounts modification in between node restart because aggressive online accts caching.

Fixed by comparing the voting data for existing and new accounts when updating the ledger db.

Test Plan

Added a new unit test exercising both cases.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 51.70%. Comparing base (558bcc3) to head (0cac60a).
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6295      +/-   ##
==========================================
+ Coverage   51.69%   51.70%   +0.01%     
==========================================
  Files         649      649              
  Lines       86858    86860       +2     
==========================================
+ Hits        44901    44915      +14     
+ Misses      39094    39089       -5     
+ Partials     2863     2856       -7     

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