fix(kselect): fix items watcher and only update if changed [KHCP-4425]

[adamdehaven]

Summary

• Only trigger the items watcher if the items changed
• Ensure every item always has a selected property (boolean)
• Prevent the item.key from having extra -selected text appended if already selected

Vue 3

Did you create a corresponding PR to add this change to the beta branch? (required)

• Yes, here is a link to the PR: fix(kselect): update items and filter logic #751
• No, I did not create a PR for the beta branch and I have added the port to beta branch tag to this PR.
• No, because [type your reasons]

If you have questions, tag @adamdehaven or @kaiarrowood.

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PR Checklist

• Does not introduce dependencies
• Functional: all changes do not break existing APIs and if so, bump major version.
• Tests pass: check the output of yarn test packages/
• Naming: the files and the method and prop variables use the same naming conventions as other Kongponents
• Framework style: abides by the essential rules in Vue's style guide
• Cleanliness: does not have formatting issues, unused code (e.g., console.logs), or leftover comments
• Docs: includes a technically accurate README, uses JSDOC where appropriate

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