Add ruff for linting instead of flake8 and isort

[maxdymond]

No description provided.

[Copilot]

Pull request overview

This PR migrates the project’s Python linting from flake8/isort to Ruff, updates configuration accordingly, and refactors the changelog renderers to share common rendering logic while adding/adjusting type annotations and docstrings to satisfy the new lint rules.

Changes:

• Replace flake8/isort tox envs with a Ruff tox env and add ruff.toml configuration.
• Remove several dev tooling dependencies (flake8/isort/bandit/etc.) and add Ruff to the dev dependency group.
• Refactor Slack/Teams changelog renderers to use a new shared render_block_document helper and tighten typing/docstrings across code and tests.

Reviewed changes

Copilot reviewed 12 out of 13 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
tox.ini	Switch tox lint env from flake8/bandit to Ruff; updates GH Actions env mapping.
ruff.toml	Adds Ruff lint/format configuration (including import sorting, docstrings, annotations, security rules).
pyproject.toml	Updates dev dependencies to include Ruff and removes legacy linters; adds basic mypy config.
setup.cfg	Removes flake8 configuration section.
src/announcer/common.py	Introduces shared rendering helpers and list utilities used by renderers.
src/announcer/changelogrenderer.py	Refactors Slack renderer to use shared helper and adds typing/docstrings.
src/announcer/teamschangelogrenderer.py	Refactors Teams renderer to use shared helper and adds typing/docstrings.
src/announcer/__init__.py	Updates mistletoe Document usage and improves typing/docstrings.
tests/test_announce.py	Reorders imports, adds typing/docstrings, and minor test data fixes.
tests/test_changelog.py	Adds module/function docstrings and typing; minor string literal cleanup.
CONTRIBUTING.md	Updates contributor instructions to reference Ruff instead of flake8.
CHANGELOG.md	Notes the Ruff migration in the Unreleased section.

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