Handle partial measurement failures and automate releases

[mktbsh]

Summary

• continue on partial measurement failures, surfacing warnings and null/N/A values instead of silently treating missing samples as zero
• harden Cloudflare measurement internals with validated phase specs, explicit response parsing, and regression coverage for warning/fallback paths
• add release-please + GoReleaser automation for version/changelog PRs and tagged artifact publishing
• ignore local agent metadata and remove the demo tape artifact from version control

Testing

• go test ./...
• go vet ./...