Use ahash in cost tracker

[tao-stones]

Problem

cost_tracker uses HashMap to keep tracking writable accounts CUs. HashMap isn't fast.

Summary of Changes

• Add benchmarking test for cost_tracker
• Use ahash for better performance

Fixes #

[tao-stones]

Master:

test bench_cost_tracker_contentious_transaction     ... bench:  11,625,587 ns/iter (+/- 254,789)
test bench_cost_tracker_non_contentious_transaction ... bench:  17,255,980 ns/iter (+/- 391,458)

This PR:

test bench_cost_tracker_contentious_transaction     ... bench:   3,587,329 ns/iter (+/- 85,738)
test bench_cost_tracker_non_contentious_transaction ... bench:   6,096,914 ns/iter (+/- 163,584)

[apfitzge]

CostTracker is not serialized on bank. We do not need consistency in hash across cluster. This will speeds up hashing, so an easy win.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.1%. Comparing base (aa2f078) to head (231e2f5).
Report is 44 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff            @@
##           master    #1252     +/-   ##
=========================================
- Coverage    82.1%    82.1%   -0.1%     
=========================================
  Files         886      886             
  Lines      236417   236424      +7     
=========================================
- Hits       194266   194253     -13     
- Misses      42151    42171     +20