fix(synonyms/curation): fix nested item access for synonym sets and curation sets

[tharropoulos]

Change Summary

• add support for accessing sub-resources as items['id'] instead of `->getItems()['id']
• keep getItems support to not break backwards compatibility
• update php version in ci to 8.4
• add classes for synonym set items, and access them through synonym set by using __get()
• add tests for clusters running v30+

PR Checklist

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[jasonbosco]

Published in v6.1.0-RC1