Limit the number of buckets in verifiedTransactionCache to 3

[tolikzinovyev]

Summary

The number of buckets in verifiedTransactionCache can be arbitrarily large depending on the requested cache size, and each lookup in the cache does that many map lookups. This PR limits the number of buckets to 3. Now, the lookup takes at most 3 lookups and the size overhead is 1.5.

Test Plan

Modified existing unit tests.

[codecov-commenter]

Codecov Report

Merging #2775 (414d931) into master (8ef8821) will decrease coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2775      +/-   ##
==========================================
- Coverage   47.10%   47.07%   -0.04%     
==========================================
  Files         349      349              
  Lines       56352    56352              
==========================================
- Hits        26543    26526      -17     
- Misses      26836    26848      +12     
- Partials     2973     2978       +5     

Impacted Files	Coverage Δ
data/transactions/verify/verifiedTxnCache.go	77.55% <100.00%> (ø)
crypto/merkletrie/trie.go	66.42% <0.00%> (-2.19%)	⬇️
crypto/merkletrie/node.go	91.62% <0.00%> (-1.87%)	⬇️
ledger/blockqueue.go	82.18% <0.00%> (-1.73%)	⬇️
catchup/peerSelector.go	98.95% <0.00%> (-1.05%)	⬇️
catchup/service.go	68.57% <0.00%> (-0.78%)	⬇️
network/wsPeer.go	75.20% <0.00%> (-0.28%)	⬇️
ledger/acctupdates.go	62.46% <0.00%> (-0.09%)	⬇️
network/wsNetwork.go	60.92% <0.00%> (ø)

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[tsachiherman]

could you take a look to see why it's failing on travis ?

[tolikzinovyev]

Flaky tests I guess. I restarted the job.

[tolikzinovyev]

Passed now!