refactor(mempool_test_util): rename constructor

[giladchase]

This constructor name hints better that its only useful for accounts.

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This change is 

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 14.62%. Comparing base (b0cfe82) to head (d6b8119).
Report is 205 commits behind head on main.

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Flag	BASE (b0cfe82)	HEAD (d6b8119)
	3	1

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1123       +/-   ##
===========================================
- Coverage   74.18%   14.62%   -59.57%     
===========================================
  Files         359       32      -327     
  Lines       36240     2783    -33457     
  Branches    36240     2783    -33457     
===========================================
- Hits        26886      407    -26479     
+ Misses       7220     2356     -4864     
+ Partials     2134       20     -2114     

Flag	Coverage Δ
	14.62% <ø> (-59.57%)	⬇️

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[ayeletstarkware]

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @elintul)

[elintul]

Reviewed 1 of 1 files at r1, all commit messages.
Reviewable status: complete! all files reviewed, all discussions resolved (waiting on @giladchase)