feat: create extendable sync states

[tonai]

Extends createSyncState to allow custom external synchronization.

the goal is to solve the problem with synchronization using static builds:

• Presenter sync in GitHub pages #855
• Supporting Synchronization for Slidev Deployments in Production Environments #1227

This can be a quick solution before migrating on Nuxt.

I am already working on an addon that will allow synchronization of shared and drawings states (and possibly others).

• The addon: https://github.com/Smile-SA/slidev-addon-sync
• The SSE and WS server that can be used for the synchronization: https://github.com/Smile-SA/slidev-sync-server

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[pkg-pr-new]

Open in Stackblitz

create-slidev-theme

pnpm add https://pkg.pr.new/slidevjs/slidev/create-slidev-theme@1854

create-slidev

pnpm add https://pkg.pr.new/slidevjs/slidev/create-slidev@1854

@slidev/client

pnpm add https://pkg.pr.new/slidevjs/slidev/@slidev/client@1854

@slidev/parser

pnpm add https://pkg.pr.new/slidevjs/slidev/@slidev/parser@1854

@slidev/cli

pnpm add https://pkg.pr.new/slidevjs/slidev/@slidev/cli@1854

@slidev/types

pnpm add https://pkg.pr.new/slidevjs/slidev/@slidev/types@1854

commit: d77ac03

[tonai]

For information I also updated my slidev poll addon https://github.com/Smile-SA/slidev-component-poll that uses createSyncState to now let https://github.com/Smile-SA/slidev-addon-sync handle the synchronization for static builds and it works just fine.
I am just waiting for this PR to be merged and a new release to be published to publish both slidev-component-poll and slidev-addon-sync with the correct slidev peerDependencies