Investigate 6.0 vs 7.0 perf

Since the perf benchmarks were updated to track .NET 6.0 and .NET 7.0 back in November, 6.0 has been showing consistently better results on most benchmarks. Why?

Interestingly, Miha's 0-byte-read change that caused a big improvement in most charts did not affect the 7.0 10240 benchmark. Why not?

The one benchmark showing better 7.0 results is 102400. The 0-byte-read change had a very out-sized impact on 7.0.

Others:
h2-h2 is similar or better on 7.0.
h2-http 1024 is better on 7.0, but 10240 and 102400 are much worse, and likely regressed by the 0-byte read change.
https-http 10240 6.0 looks improved by the 0-byte-read change, but 7.0 regressed.