perf(*): reduce subschema memory usage

[bungle]

Summary

This reduces memory usage of Kong worker on start from ~76MB to ~71MB in dbless/data plane scenarios (on EE the reduction is bigger as there are more bundled plugins by default).

No need to cherry-pick as there is already: https://github.com/Kong/kong-ee/pull/10150

KAG-5292

Checklist

• [ ] ~The Pull Request has tests~
• [x] A changelog file has been created under changelog/unreleased/kong or skip-changelog label added on PR if changelog is unnecessary. README.md
• [ ] ~There is a user-facing docs PR against https://github.com/Kong/docs.konghq.com - PUT DOCS PR HERE~