Prometheus v3.16.0 Tightens PromQL, Remote Write

This is a maintenance-heavy release with meaningful correctness and operator-facing changes across PromQL, storage, and telemetry pipelines.

• –The experimental integral() function brings area-under-the-curve calculations directly into PromQL.
• –Query statistics now account for subquery work, improving observability into expensive queries.
• –Remote Write 2.0 users must adjust dashboards as deprecated metadata metrics disappear.
• –Stronger validation rejects malformed exemplars and native histograms instead of persisting corrupt data.
• –TLS-enabled deployments now default external URLs to HTTPS, reducing a common configuration footgun.