Each run_n call now collects ITERS × SETS raw samples across all sets
(one warmup before the first set, discarded), then takes a single global
median. Previously only ITERS=15 samples were taken per bench invocation,
which produced noisy results in sweep.py regress.
SMARM_BENCH_SETS is read from the environment; the default of 5 gives
75 samples per bench row (5×15), matching the stability of the multi-run
bash approach without requiring multiple cargo bench invocations.
Also moves scripts/bench_rq.sh into benches/ alongside sweep.py.
The cd "$(dirname "$0")/.." path logic is unchanged.
