[charlesvien]

💡 Motivation and Context

Catches up with posthog-unity and PostHog/sdk-specs.

• Rename projectKey to projectToken per the setup spec. projectKey never shipped and apiKey still works.
• Init warns and skips setup when the token is blank instead of erroring.
• Add beforeSend to modify or drop events.
• Retry flag requests on network errors and 502/504 (featureFlagRequestMaxRetries, default 1).
• Queue: retry 408/429, drop single events rejected with 413 and only remove events that were actually sent.
• Bump dtolnay/rust-toolchain in the release workflow (replaces Bump dtolnay/rust-toolchain from 7e38f4b43b4db5c8dd498af069a4f6196df1d067 to e2a55d2ffb04f378e9626c28d38b36d230d1e12f #23).

💚 How did you test it?

Unit tests, selene, stylua and rojo build pass. Not tested in Studio.

📝 Checklist

• I reviewed the submitted code.
• I added tests to verify the changes.
• I updated the docs if needed.
• No breaking change or entry added to the changelog.

If releasing new changes

• Added a changeset file in .sampo/changesets/

🤖 Agent context

Autonomy: Human-driven (agent-assisted)

Written with Claude Code by diffing posthog-unity since June against this repo. Skipped Unity's User-Agent header since Roblox may block it.