Switch to uv for dev workflow

[lordmauve]

Summary

• add optional dev dependencies to pyproject.toml
• use uv for tox and CI setup
• document uv in contributing guide
• drop old requirements files
• allow uv commands in tox

Testing

• pre-commit run --files .github/workflows/test.yml doc/contributing.rst pyproject.toml tox.ini
• xvfb-run --auto-servernum tox -e py,flake8

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https://chatgpt.com/codex/tasks/task_e_68416cc831488328b058abd42c32dee7

[Copilot]

Pull Request Overview

This PR updates the development workflow by switching from the old pip‐based commands to a new uv-based workflow. Key changes include:

• Updating tox.ini to replace pip commands with uv commands.
• Moving dev dependency definitions from requirements-dev.txt to pyproject.toml.
• Modifying the contributing docs and CI workflow to reflect the new uv-based commands.

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tox.ini	Uses uv for installing dependencies and running tests, replacing legacy pip commands.
requirements-dev.txt	Removed as dev dependencies are now managed via pyproject.toml dependency groups.
pyproject.toml	Introduces a dev dependency group with tools like tox, pytest, and flake8.
doc/contributing.rst	Updates instructions to use uv sync for locally-editable installs and test running command change.
.github/workflows/test.yml	Incorporates steps for installing uv and syncing dependencies using uv in the CI workflow.