grand_central_m4(feat): Adding i2c example

[supersimple33]

Summary

This code won't compile but it would when targeting the new hal version.

Checklist

• All new or modified code is well documented, especially public items
• No new warnings or clippy suggestions have been introduced - CI will deny clippy warnings by default! You may #[allow] certain lints where reasonable, but ideally justify those with a short comment.

[jbeaurivage]

Marking this as draft for the time being, since it's waiting on a HAL release.