Support # | for quarto metadata blocks

[gadenbuie]

Originally reported by @mcanouil in quarto-ext/shinylive#67.

Python formatter do not like #| and will format to # |.
In regular Python code cells, Quarto supports this because of the above limitation.

The Shinylive extension on the other hand does not.

---
title: "Quarto Playground"
format: html
---

```{shinylive-python}
# | standalone: true

from shiny import *

app_ui = ui.page_fluid(
    ui.input_slider("n", "N", 0, 100, 40),
    ui.output_text_verbatim("txt"),
)


def server(input, output, session):
    @output
    @render.text
    def txt():
        return f"The value of n*2 is {input.n() * 2}"


app = App(app_ui, server)
```

[gadenbuie]

Problematic line:

shinylive/src/parse-codeblock.ts

Line 102 in 6975f07

if (!line.match(/^#\| /)) {