Sphinx Substitution Extensions

Sphinx Substitution Extensions enhances Sphinx documentation by enabling variable substitutions within standard directives like `code-block`, `literalinclude`, and `image`, and introduces an inline `substitution-code` role. It supports both reStructuredText (reST) and MyST Markdown syntax for defining and using substitutions. The project maintains a frequent release cadence, often with multiple updates per month, ensuring continuous improvements and compatibility.