✨ feat: enable adding URL/path to code blocks

[welpo]

Summary

Adds a add_src_to_code_block shortcode with its corresponding—sadly necessary—JavaScript. This allows showing a path or URL on a code block.

Related issue

Resolves #304.

Changes

• Add the shortcode to add an invisible span with the src.
• Add JavaScript to show this src on the next code block found. If it's a URL, it makes it an <a> tag.
• Updates debugging code.
• Updates documentation.

Accessibility

Uses semantic HTML. Tested with VoiceOver on macOS.

Screenshots

Example usage with the remote text shortcode:

{{/* add_src_to_code_block(src="https://raw.githubusercontent.com/welpo/doteki/main/.gitignore") */}}
```.gitignore
__pycache__/
*coverage*
.vscode/
dist/
```

Type of change

• Bug fix (fixes an issue without altering functionality)
• New feature (adds non-breaking functionality)
• Breaking change (alters existing functionality)
• UI/UX improvement (enhances user interface without altering functionality)
• Refactor (improves code quality without altering functionality)
• Documentation update
• Other (please describe below)

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Checklist

• I have verified the accessibility of my changes
• I have tested all possible scenarios for this change
• I have updated theme.toml with a sane default for the feature
• I have made corresponding changes to the documentation:
  • Updated config.toml comments
  • Updated theme.toml comments
  • Updated "Mastering tabi" post in English
  • (Optional) Updated "Mastering tabi" post in Spanish
  • (Optional) Updated "Mastering tabi" post in Catalan