feat(editor): add collapse/expand functionality to code block component (#14884)

This PR fixes #14040 

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* Code blocks can be collapsed and expanded via a toolbar toggle
(visible when the document is editable).
* Collapsed code blocks show a limited preview (~8 lines) with a bottom
fade overlay and reduced padding.
* Toolbar button updates icon and tooltip to reflect collapsed/expanded
state.
* Collapse state is preserved on the block so its current
collapsed/expanded setting is retained.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

blocksuite/affine/model/src/blocks/code/code-model.ts

@@ -14,6 +14,7 @@ type CodeBlockProps = {
   caption: string;
   preview?: boolean;
   lineNumber?: boolean;
+  collapsed?: boolean;
   comments?: Record<string, boolean>;
 } & BlockMeta;
 
@@ -27,6 +28,7 @@ export const CodeBlockSchema = defineBlockSchema({
       caption: '',
       preview: undefined,
       lineNumber: undefined,
+      collapsed: undefined,
       comments: undefined,
       'meta:createdAt': undefined,
       'meta:createdBy': undefined,