Redis Window Metrics: smaller event keys

[bolshakov]

Further reduces amount of data stored as ZSET members for window metrics. Benchmark results in. At 15,000 members (50 req/s, 300s window):

approach	KB	bytes/member
hex-24 (SecureRandom)	1,730 KB	118
int-seq (HINCRBY)	1,494 KB	102
savings	~236 KB/ZSET	~16

Performance benchmark results: difference falls withing noise

[github-actions]

Review price tag

🟢 37 effective lines — about 5–11 min (down from 43–107 min) of focused review (based on 200–500 lines/hour). This is within the range where reviewers find the most issues per line, and small changes usually receive feedback the fastest.

Why these numbers?

These minutes are what careful defect-finding costs at 200–500 lines/hour — the rate review studies report, not how long a skim takes. "Effective lines" already exclude generated files and lockfiles. Treat the rates and the 200/400 thresholds as guardrails, not laws.

[bolshakov]

Replaced by #904