txHandler: fix TestTxHandlerAppRateLimiter

[algorandskiy]

Summary

As discovered in #5972 the TestTxHandlerAppRateLimiter had a typo.
This PR fixed it by crafting workload to make sure ARL in txHandler is getting actually called.

While debugging I noticed that maxBucketSize is set to 1 if TxBacklogAppTxRateLimiterMaxSize is less than 128 (number of buckets). Although this was not an issue in production due to TxBacklogAppTxRateLimiterMaxSize=1048576 it would trigger eviction on each insert that makes ARL noop. Setting maxBucketSize to 2 as its min value makes it working in such extreme configuration.

Test Plan

This is a test fix

Closes #5972

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 56.27%. Comparing base (75bb6a9) to head (fb7d825).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6075      +/-   ##
==========================================
- Coverage   56.29%   56.27%   -0.03%     
==========================================
  Files         488      488              
  Lines       69581    69581              
==========================================
- Hits        39172    39156      -16     
- Misses      27752    27764      +12     
- Partials     2657     2661       +4     

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