Support for running nbqa on quatro format (.qmd) markdown files

[hguturu]

Closes #880

Two main changes:

• Added check for .qmd when using Jupytext
• Added conversion of leading quartro cell options #| that get changed to # | by black/ruff back to #|
  (_restore_quarto_cell_options) - in theory this can be dropped if black and ruff natively support this format
  • black is evaluating how to handle this situation - Exceptions to comment spacing psf/black#3668
  • ruff also has the issue - Add support for Quarto notebooks  astral-sh/ruff#6140
  • No longer needed since Quarto authors confirm it can handle both #| and # | for python due to formatters - Quarto Cell Options Specification quarto-dev/quarto-cli#12364 (comment)
• Added test_jupytext.test_qmd and supporting resource tests/data/notebook_for_testing.qmd to test new functionality
• Updated README.md with .qmd support feature
• Updated requirements-dev.txt and setup.cfg with quarto-cli dependency

20250324:

• Refactored usage of _restore_quarto_cell_options so other formats don't break
  • Removed logic all together since both #| and # | are supported
• Discovered new cell option behavior and checking quarto team if valid behavior or bug in quarto - Quarto Cell Options Specification quarto-dev/quarto-cli#12363
  • Test case added for new multi-line cell options

PR simplified to just checking .qmd extension since special handling logic for quarto #| are no longer needed. Authors also confirm {python} is required for runable code blocks (the same ones we format) quarto-dev/quarto-cli#12364 (reply in thread). All other cases of references to python are test with syntax highlighting.

Code tested locally with tox -e py and all tests passing, so should be ready for another round of github actions.