Integrate with `IORuntime` metrics

[armanbilge]

Linking to typelevel/cats-effect#3038 which will land in 3.4.0. Since Cats Effect is a core dependency of otel4s it would be nice to offer this out-of-the-box.

[iRevive]

There is a basic implementation available typelevel/cats-effect#3317.

On the otel4s side, we should use observable (async) metrics #158.