testing: add config flag for ARL to count all messages

[cce]

Summary

Following on #6167 this provides a configuration option (default disabled) to feed messages dropped by ERL (EnableTxBacklogRateLimiting) into ARL (EnableTxBacklogAppRateLimiting), so that all TX messages are counted by ARL, not just the ones that made it past the first pass of ERL's rate limiter.

Test Plan

Merging into a testing feature branch — existing tests should pass.

[codecov]

Codecov Report

Attention: Patch coverage is 25.00000% with 3 lines in your changes missing coverage. Please review.

Project coverage is 56.27%. Comparing base (cc8dbb7) to head (86e51f0).
Report is 1 commits behind head on experimental-tweaks.

Files with missing lines	Patch %	Lines
data/txHandler.go	25.00%	3 Missing ⚠️

Additional details and impacted files

@@                   Coverage Diff                   @@
##           experimental-tweaks    #6168      +/-   ##
=======================================================
+ Coverage                55.91%   56.27%   +0.36%     
=======================================================
  Files                      494      494              
  Lines                    69960    69964       +4     
=======================================================
+ Hits                     39115    39372     +257     
+ Misses                   28160    27912     -248     
+ Partials                  2685     2680       -5     

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