bookmark: use fast-deep-equal to compare bookmarks in reducer

In `packages/modules/bookmark/src/BookmarkProvider.reducer.ts`, `createBookmarkReducer` has:

```ts
/**
* Creates a reducer for managing the state of bookmarks.
*
* @todo add fast-deep-equal to compare bookmarks
* ...
*/
```

Bookmark comparisons in the reducer should use `fast-deep-equal` (already a dependency elsewhere in the framework) instead of reference/shallow equality, to avoid unnecessary state updates.

Start in packages/modules/bookmark/src/BookmarkProvider.reducer.ts at createBookmarkReducer and inspect how bookmark comparisons currently determine state updates. Use the framework's existing fast-deep-equal dependency for those comparisons, then verify that equivalent bookmark values no longer cause unnecessary updates.

Written by the indexing model from the issue text.