feat(parser): add icon support for code blocks

[mrnasil]

Summary

• Add support for icon syntax in code block meta: [filename|icon|position]
• Parse icon and iconPosition from code block syntax
• Pass icon props to ProsePre component
• Add basic icon/filename header rendering

Syntax

python [Script|logos:python|right]
print("test")

Format	Description
[filename|icon]	Filename with icon on left (default)
[filename|icon|right]	Filename with icon on right
[|icon|position]	Icon only, no filename
[filename]	Backward compatible, no icon

Test plan

• Unit tests for icon parsing added
• All existing tests pass (61/61)
• Playground example added

Notes

For full icon rendering support with @nuxt/ui, a separate PR to nuxt/ui is needed to handle iconPosition in CodeGroup.vue.

[mrnasil]

I've opened a PR in nuxt/ui that implements the UI side of this feature: nuxt/ui#5953. Also waiting for this to be merged to fully unlock the functionality. Thanks!

[mrnasil]

@farnabaz When you get a chance, can you check this out? I need a structure like this for my documentation page. Creating a custom component didn’t seem worth it. Many docs also need icons for different languages or different types of explanations, I think.

[farnabaz]

Thanks for the PR @mrnasil
However I think feature is deeply UI related and supporting/parsing icon (string) and position can be done in UI components.

You can use code block meta to pass these information to your component and use it there.

```ts icon="logos:nuxt" 
Your awesome code example
```

And in meta props of ProsePre component you will get icon="logos:nuxt". with a simple logic values can be extracted.

I'm closing this PR in favor of meta prop.