- Add GetEcosystemStats, aggregating packages, versions, artifacts,
cache size, downloads and downloaded bytes per ecosystem
- Publish six proxy_ecosystem_* gauges from it on the existing
one-minute cache-stats tick
- Set and selectively delete rather than Reset, so no scrape lands on
a half-populated vector
- Report artifacts with no package row under "unattributed" rather
than dropping them, so the figures still add up
Part 2 of 6 splitting #381 up.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>