Function render 

pub fn render(d: Duration) -> String

Render a Duration in the canonical pleme-io duration string form ("30s", "1m", "1h", "500ms"). The same form every caixa typed-duration slot serializes to and the same form K8s Gateway API HTTPRoute timeouts / backendRequest and Cilium EnvoyConfig per-route timeouts both expect (an integer followed by s/m/h/ms, no fractional values, no leading +). Lifted to pub so caixa-side renderers (caixa-mesh::gateway_routes’s :politicas :timeout overlay, the future per-:politicas CiliumClusterwideEnvoyConfig emitter, the future caixa-otel collector pipeline emitter) can consume the same canonical formatter without re-inlining the magnitude/unit decision tree (and inheriting the same drift footguns: a subtly different 300ms vs 0.3s rendering breaks downstream apply-time parsing in non-obvious ways).