Transformers not working properly with YAML comments

[brc-dd]

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Describe the bug

Follow up on #934

Downstream issue: vuejs/vitepress#4729 (comment)

Edit: Probably same as #1006

this doesn't work:

```yaml
# foo # [!code ++] [!code focus]
```

this works:

```yaml
# foo // [!code ++] [!code focus]
```

this leaves dangling `#`

```yaml
foo # bar # [!code ++] [!code focus]
```

Reproduction

https://stackblitz.com/edit/vite-gbsar3e7?file=docs/index.md

Contributes

• I am willing to submit a PR to fix this issue
• I am willing to submit a PR with failing tests