Support cache for list

[JiuqingSong]

Content Model cache was not working for list and list items because they are too complex. But when adding long enough content under list, we still need the cache to help improve editing performance, otherwise every time we do format change, the whole list need to be rebuilt.

In this change I start to enable cache for list and list item. It is under a new experimental feature CacheList and it is by default turned on in demo site. With this flight, all behaviors should be the same with before, but list won't be recreated unless list itself is changed

Before:

After:

[Copilot]

Pull request overview

This PR introduces caching support for list and list item elements to improve editing performance when working with long lists. The cache prevents unnecessary recreation of list structures when only formatting changes occur.

Key changes:

• Adds a new experimental feature CacheList (enabled by default in demo site)
• Introduces refNode tracking in list stack to manage element reuse
• Implements caching logic for both list containers (OL/UL) and list items (LI)

Reviewed changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
ExperimentalFeature.ts	Adds CacheList experimental feature flag
ModelToDomFormatContext.ts	Adds refNode property to track next insertion point in list stack
EditorContext.ts	Adds allowCacheListItem flag to control list caching behavior
stackFormat.ts	Preserves and restores nodeStack during format operations
cleanUpRestNodes.ts	New utility to remove remaining DOM nodes during rewrite
handleList.ts	Implements caching logic for list container elements (OL/UL)
handleListItem.ts	Implements caching logic for list item elements (LI)
handleBlockGroupChildren.ts	Adds cleanup of list node stack between non-list blocks
createEditorContext.ts	Enables allowCacheListItem when CacheList feature is active
setListType.ts	Uses readonly types and mutateBlock for immutability
Various test files	Updates tests to include refNode: null in expectations and adds comprehensive cache tests
Demo files	Enables CacheList feature by default in demo site

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