txHandler: fixes to ERL resources management

[algorandskiy]

Summary

ERL's capguard was not disposed properly in some scenarios that leaded to under or over provisioned capacity.

Test Plan

Added a unit test.

[codecov]

Codecov Report

Attention: Patch coverage is 71.42857% with 2 lines in your changes missing coverage. Please review.

Project coverage is 55.97%. Comparing base (6c91f52) to head (45b899c).
Report is 19 commits behind head on master.

Files	Patch %	Lines
data/txHandler.go	71.42%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6019      +/-   ##
==========================================
+ Coverage   55.94%   55.97%   +0.02%     
==========================================
  Files         482      482              
  Lines       68310    68317       +7     
==========================================
+ Hits        38219    38242      +23     
+ Misses      27500    27485      -15     
+ Partials     2591     2590       -1     

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