Removing unnecessary mutex in the bank client code

[godmodegalactus]

Problem

There is a unnecessary mutex in bank client code, the transaction crossbeam sender locked behind the mutex.

Summary of Changes

Removing the mutex and cloning the sender instead is a better solution.

Fixes #

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.8%. Comparing base (a764514) to head (6a5a312).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6133   +/-   ##
=======================================
  Coverage    82.8%    82.8%           
=======================================
  Files         842      842           
  Lines      377392   377391    -1     
=======================================
  Hits       312832   312832           
+ Misses      64560    64559    -1     

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[KirillLykov]

Is this client used anywhere these days?