feat: super properties for posthog-node

[harshit078]

Problem

• This PR address issue https://github.com/PostHog/posthog-js/issues/2727
• added super properties in posthog-node

Changes

• added registeredProperties in prepareEventMessage
• this allows prepareEventMessage to ensure that every event includes globally registered super properties.
• Added tests to verify the correct behavior of property registration and overriding.

Release info Sub-libraries affected

Libraries affected

• [ ] All of them
• [ ] posthog-js (web)
• [ ] posthog-js-lite (web lite)
• [x] posthog-node
• [ ] posthog-react-native
• [ ] @posthog/react
• [ ] @posthog/ai
• [ ] @posthog/nextjs-config
• [ ] @posthog/nuxt
• [ ] @posthog/rollup-plugin
• [ ] @posthog/webpack-plugin

Checklist

• [x] Tests for new code
• [ ] Accounted for the impact of any changes across different platforms
• [x] Accounted for backwards compatibility of any changes (no breaking changes!)
• [x] Took care not to unnecessarily increase the bundle size

If releasing new changes

• [ ] Ran pnpm changeset to generate a changeset file
• [ ] Added the "release" label to the PR to indicate we're publishing new versions for the affected packages

[vercel[bot]]

@harshit078 is attempting to deploy a commit to the PostHog Team on Vercel.

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[harshit078]

Hey @pauldambra , can you review the PR ? Thanks !

[lucasheriques]

hey Harshit! I'll review this one tomorrow - got stuck today fixing some other issues, but it's on my list

[harshit078]

Hey @lucasheriques , sure I'll do the 3 steps and update the PR. Thanks !