Lang support for code block

A `$Lang` argument in code block so we can write something like this

CodeBlock -Lang ps1 -Code @'
Install-Module XpandPosh
'@

and output
```ps1

Install-Module XpandPosh

```

Start by locating the CodeBlock entry point in the PowerShell DSL and inspect how its arguments are turned into Markdown. Verify the requested -Lang ps1 and -Code syntax produces a fenced code block with the matching language tag, using the example output as the completion check.

Written by the indexing model from the issue text.