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.