Add support for shiny mode magic comment

[wch]

Intent

This PR adds support for shiny mode magic comments which are generated by interactive Quarto dashboards that use Shiny for Python. This change allows users to create Quarto dashboards that have from shiny.express import ... instead of from shiny ...; previously those apps would not run.

See the following for more information:

• Add support for Shiny Express in Quarto Dashboards, take 2 py-shiny#1217
• Change imports from shiny to shiny.express quarto-dev/quarto-web#1049

Type of Change

• Bug Fix
• New Feature
• Breaking Change

Approach

This copies over code from the py-shiny repository, from this file:

https://github.com/posit-dev/py-shiny/blob/2b66c898cb9d0fc827e587b11a839e270b2e814f/shiny/express/_is_express.py

Directions for Reviewers

Checklist

• I have updated CHANGELOG.md to cover notable changes.
• I have updated all related GitHub issues to reflect their current state.

[wch]

The linting test is failing because in Python 3.7, the typing module doesn't have Literal. (It is present in 3.8+.)

I could work around this by importing from typing_extensions. That said, my understanding is that we've dropped Python 3.7 support, so can we stop testing on that platform?

[github-actions]

☂️ Python Coverage

current status: ✅

Overall Coverage

Lines	Covered	Coverage	Threshold	Status
4558	3274	72%	0%	🟢

New Files

No new covered files...

Modified Files

File	Coverage	Status
rsconnect/shiny_express.py	75%	🟢
TOTAL	75%	🟢

updated for commit: 3126880 by action🐍

[mmarchetti]

rsconnect-python hasn't removed Python 3.7 support, but Connect has removed it so it's probably time.

[nealrichardson]

rsconnect-python hasn't removed Python 3.7 support, but Connect has removed it so it's probably time.

I made #556 for that.

[nealrichardson]

Would it be worth adding a test for this function?

[wch]

I've added tests for Shiny Express app detection in general in cc3766e.

[aronatkins]

@wch - if you pull in master, you should see CI pass.