Add dropped records SLO to UC2/UC4 (no Samza)

See merge request !310

(Samza does not provide all metrics we require and additionally, we would need to convert Samza metrics first)

additionally, do some minor code cleanup

Bumps [nokogiri](https://github.com/sparklemotion/nokogiri) from 1.13.9 to 1.13.10.
- [Release notes](https://github.com/sparklemotion/nokogiri/releases)
- [Changelog](https://github.com/sparklemotion/nokogiri/blob/main/CHANGELOG.md)
- [Commits](https://github.com/sparklemotion/nokogiri/compare/v1.13.9...v1.13.10

)

---
updated-dependencies:
- dependency-name: nokogiri
  dependency-type: indirect
...

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