otel/instrument-routes wraps each flattened Dream route's handler in a timed
span named METHOD /route with {:http.method :http.route :http.status} attrs;
host/make-app applies it so every matched request becomes a trace. Refactored
with-span onto a shared otel/-timed core that takes a finalize fn for
result-derived attrs (the http.status only known post-handler).
Clamp against a high-water mark so the clock never steps backwards; span
durations stay non-negative. Real ns-scale timestamps replace the P1
placeholder counter.
