Simplifies `JoinKeys` from R6 to S3 list-like object #670

Job	Run time
Version Bump 🤜🤛	0s
Audit Dependencies 🕵️‍♂️ / oysteR scan 🦪	1m 31s
Coverage 📔 / Coverage 📔	3m 7s
Coverage 📔 / Covtracer 🐄	0s
gitleaks 💧 / gitleaks 💧	6s
gitleaks 💧 / PII Check 💳	0s
License Check 🃏 / Check 🚩	39s
Check URLs 🌐 / Validate Links 🔎	4s
SuperLinter 🦸‍♀️ / SuperLinter 🦸‍♂️	1m 37s
SuperLinter 🦸‍♀️ / Lint R code 🧶	1m 39s
Roxygen 🅾 / Manual pages check 🏁	1m 49s
R CMD Check 🧬 / ghcr.io/insightsengineering/rstudio, version latest	4m 8s
Spell Check 🆎 / Check spelling 🔠	1m 33s
Style Check 👗 / Check code style 🔠	2m 0s
Version Check 🏁 / Emoji in NEWS.md 📰	4s
Version Check 🏁 / Version check 🏁	2s
Coverage 📔 / Publish coverage report 📰	0s
R CMD Check 🧬 / Upload build tar.gz	0s
R CMD Check 🧬 / Publish JUnit HTML report 📰	0s
	18m 19s

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