go stats: give ties the same rank

[pro-wh]

we don't use the "Rank" column from the stats program because it's wrong on ties. we probably still can't use it directly because we often need to combine it across upgrades. but here's some logic to give ties the same rank.

[codecov]

Codecov Report

Merging #2908 into master will decrease coverage by 0.27%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2908      +/-   ##
==========================================
- Coverage   68.16%   67.88%   -0.28%     
==========================================
  Files         354      354              
  Lines       34347    34347              
==========================================
- Hits        23414    23318      -96     
- Misses       7960     8033      +73     
- Partials     2973     2996      +23     

Impacted Files	Coverage Δ
go/consensus/tendermint/api/errors.go	86.66% <0.00%> (-13.34%)	⬇️
go/storage/metrics.go	81.52% <0.00%> (-9.79%)	⬇️
go/storage/api/root_cache.go	70.11% <0.00%> (-6.90%)	⬇️
...ompute/txnscheduler/algorithm/batching/batching.go	78.66% <0.00%> (-6.67%)	⬇️
go/storage/database/database.go	75.45% <0.00%> (-5.46%)	⬇️
go/storage/mkvs/insert.go	87.75% <0.00%> (-5.45%)	⬇️
go/runtime/client/watcher.go	73.84% <0.00%> (-4.62%)	⬇️
go/consensus/tendermint/apps/staking/state/gas.go	77.08% <0.00%> (-4.17%)	⬇️
go/storage/mkvs/tree.go	89.28% <0.00%> (-3.58%)	⬇️
go/storage/client/client.go	75.33% <0.00%> (-2.65%)	⬇️
... and 22 more

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