Add stats about account format versions to util's checkpoint-collect-stats command

[fxamacker]

Updates onflow/cadence#3584
Closes #6610

This PR updates util program's checkpoint-collect-stats command to output stats about account format versions (e.g. counts for v1 vs v2).

While at it, also bump montanaflynn/stats package to the latest version.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 122 lines in your changes missing coverage. Please review.

Project coverage is 41.11%. Comparing base (b740fc0) to head (f28c711).

Files with missing lines	Patch %	Lines
...util/cmd/checkpoint-collect-stats/account_stats.go	0.00%	52 Missing ⚠️
cmd/util/cmd/checkpoint-collect-stats/cmd.go	0.00%	41 Missing ⚠️
...d/util/cmd/checkpoint-collect-stats/stats_utils.go	0.00%	29 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6882      +/-   ##
==========================================
- Coverage   41.11%   41.11%   -0.01%     
==========================================
  Files        2116     2118       +2     
  Lines      185749   185785      +36     
==========================================
+ Hits        76378    76387       +9     
- Misses     102954   102983      +29     
+ Partials     6417     6415       -2     

Flag	Coverage Δ
unittests	41.11% <0.00%> (-0.01%)	⬇️

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