Create evlog Enricher

Add a new built-in enricher to evlog. Every enricher is built on the public toolkit primitive defineEnricher from evlog/toolkit, so a community enricher has the same shape as a built-in one.

PR Title

feat(core): add the {name} enricher

Enrichers live in the core package surface (evlog/enrichers), so use the core scope unless a dedicated scope exists.

Touchpoints Checklist