Log message:
devel/ruby-metrics: add package version 0.12.1

Add package version 0.12.1, this package is required by new ruby-async
package.

Metrics

Capture metrics about code execution in a vendor agnostic way.  As the
author of many libraries which would benefit from metrics, there are few key
priorities: (1) zero overhead if metrics are disabled, minimal overhead if
enabled, and (2) a small and opinionated interface with standardised
semantics.

Features

* Zero-overhead if tracing is disabled and minimal overhead if enabled.
* Small opinionated interface with standardised semantics.