Add bracket percentile to player benchmarks

[geracosta]

Adds a pct_bracket field next to pct in the match players' benchmarks: the same percentile computed against only the matches in this match's rank bracket, using the bracket zsets from #2972. The bracket is derived from the players' average rank with getMatchRankTier, same as the write side in counts.ts. Skipped for turbo (no bracket keys) and when the bracket zset is empty, so the field is additive and consumers that don't know about it see no change.

odota/web#3373 uses it to add a line to the benchmark tooltips: "Equal or higher than X% at this match's average rank".

Note: branched on top of #2978 since both touch the same lines of getPlayerBenchmarks (the deaths_per_min inversion applies to the bracket percentile too).