Manual baseline, not a CI gate: go test -bench=. -benchmem.
First numbers on a Ryzen 7 5800X: HolmeKim ~25us/op (48KB, 671
allocs), full RunScenario ~45us/op (78KB, 681 allocs). Plenty fast
until milestone 5 runs thousands of cascades per request; this is the
'before' picture for that work.
b.Loop() (Go 1.24+) replaces the old 'for i := 0; i < b.N; i++'
pattern and prevents the compiler optimising the loop body away.
