perf(docs): coalesce changeset render refreshes

[DR-Univer]

Summary

• coalesce synchronous changeset-driven document layout refreshes into one microtask
• schedule drawing refresh only after the coalesced document layout pass
• avoid repeated document layout and drawing work while embedded Slide thumbnails settle

Why

Slide thumbnails can mount embedded documents while collaboration changesets are replayed. Refreshing layout and drawing for every synchronous changeset caused redundant work and delayed stable thumbnail capture.

Paired Pro PR

• dream-num/univer-pro#5476

Validation

• targeted Vitest coverage for the document render controller
• typecheck for @univerjs/docs-ui and @univerjs/docs-drawing-ui
• ESLint on all changed files (0 errors)
• outer repository convention checker
• git diff --check

Scope

This PR contains only the Docs rendering changes created in the paired Slide thumbnail session. Sheet low-zoom rendering work from a separate task is not included.

[github-actions]

Playwright test results

 10 passed

Details

 10 tests across 4 suites
 4 minutes, 15 seconds
 9a52fcb
 For more information, see full report and artifacts

[codecov]

Codecov Report

❌ Patch coverage is 39.13043% with 28 lines in your changes missing coverage. Please review.
✅ Project coverage is 81.05%. Comparing base (04a7e8e) to head (9a52fcb).

Files with missing lines	Patch %	Lines
...rollers/doc-drawing-transform-update.controller.ts	0.00%	25 Missing ⚠️
...ollers/render-controllers/doc.render-controller.ts	85.71%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #7477      +/-   ##
==========================================
- Coverage   81.06%   81.05%   -0.01%     
==========================================
  Files        2689     2689              
  Lines      167226   167259      +33     
  Branches    41046    41299     +253     
==========================================
+ Hits       135562   135575      +13     
- Misses      31612    31632      +20     
  Partials       52       52              

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