Support `# |` for quarto metadata blocks

Originally reported by @mcanouil in https://github.com/quarto-ext/shinylive/issues/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)
```

Start by locating the Shinylive extension's handling of Quarto metadata blocks and existing tests for #| parsing. Reproduce the example with # | standalone: true; done means the shinylive-python block accepts the spaced marker and preserves the expected standalone behavior. The issue names no file or test, so repository search is needed first.