feat: add markdown export from synced doc block

[L-Sun]

Closes: BS-665

TL;DR

This PR adds support for exporting synced documents using embedSyncedDocMiddleware with MakrdownAdapter.

Example

const job = new Job({
  collection,
  middlewares: [embedSyncedDocMiddleware('content')],
});
const adapter = new MarkdownAdapter(job);
// Do what you want to exporting here using markdown adapter
const content = adapter.fromSliceSnapshot({snapshot});

There is a output example that export doc -> synced doc -> nested synced doc

# Doc

Hello, I' m Doc

// Begin: Embed synced doc block, export all content of synced doc
# Synced Doc

Hello, I'm Synced Doc

// Begin: Nested embed synced doc block, just export it's title
Nested Doc
// End: Nested embed synced doc block 
// End: Embed synced doc block

What changed?

1. Transformers: Updated middlewares to include embedSyncedDocMiddleware.
2. MarkdownAdapter: Added logic to handle 'embedSyncedDoc' nodes.
3. Job Class: Added collection getter.
4. Tests: Added unit tests for the synced-doc export logic.
5. Uint Test Utilities: Modified createJob to accept middlewares and initialize with AffineSchemas.

Why make this change?

To enable loading content of embed-synced-doc for AI context. Related issue: BS-632

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[L-Sun]

• #7405 👈
• master

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Merge activity

• Jun 24, 7:26 AM EDT: The merge label 'merge' was detected. This PR will be added to the Graphite merge queue once it meets the requirements.
• Jun 24, 7:27 AM EDT: L-Sun added this pull request to the Graphite merge queue.
• Jun 24, 7:38 AM EDT: L-Sun merged this pull request with the Graphite merge queue.