Document syncing layer change callback across halves

[BlueDrink9]

Description

Types of Changes

• Core
• Bugfix
• New feature
• Enhancement/optimization
• Keyboard (addition or update)
• Keymap/layout/userspace (addition or update)
• Documentation

Issues Fixed or Closed by This PR

Checklist

• My code follows the code style of this project: C, Python
• I have read the PR Checklist document and have made the appropriate changes.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• I have tested the changes and verified that they work and don't break anything (as well as I can manage).

[lesshonor]

I'm not going to weigh in on whether this is worth putting into the QMK docs one way or the other, but you might want to try this less-complex suggestion:

tzarc: In housekeeping keep track of the last seen state, if it changes invoke a callback?
tzarc: State is already synced as you said, compare and exec

[BlueDrink9]

Thanks, just saw that. It looks like a better solution so I'll test.

I might keep this code but move it to the split docs, because more (and simpler) examples of how to use split comms will be helpful

[github-actions]

Thank you for your contribution!
This pull request has been automatically marked as stale because it has not had activity in the last 45 days. It will be closed in 30 days if no further activity occurs. Please feel free to give a status update now, or re-open when it's ready.
For maintainers: Please label with bug, awaiting review, breaking_change, in progress, or on hold to prevent the issue from being re-flagged.

[BlueDrink9]

waiting for a review after my last changes. Sorry, should probably have commented that they were made.

[github-actions]

Thank you for your contribution!
This pull request has been automatically marked as stale because it has not had activity in the last 45 days. It will be closed in 30 days if no further activity occurs. Please feel free to give a status update now, or re-open when it's ready.
For maintainers: Please label with bug, awaiting review, breaking_change, in progress, or on hold to prevent the issue from being re-flagged.

[BlueDrink9]

Still waiting after fixing the image issue