//! Macros shared across runtime implementations.
/// Prepare metrics for a spawned task.
///
/// Returns a `(Label, MetricHandle)` pair for tracking spawned tasks.
///
/// The `Label` identifies the task in the metrics registry and the
/// `MetricHandle` immediately increments the `tasks_running` gauge for that
/// label. Call `MetricHandle::finish` once the task completes to decrement the
/// gauge.