chore(ci): replace black and flake8/Hound CI with ruff

[ceache]

Addresses #774

Summary

This PR modernizes Kazoo's linting, formatting, and PR review workflow:

1. Ruff Migration: Replaces Black and Flake8 with Ruff (pinned to 0.16.7), unifying linting and formatting under a single tool.
2. HoundCI Retirement & Reviewdog Replacement: Retires HoundCI in favor of Reviewdog, delivering fast and reliable inline comments on PR diffs directly within GitHub Actions.
3. CI & Tox Optimization: Replaces the multiple separate black and pep8 tox virtualenvs in CI with a single unified ruff environment, significantly speeding up validation runs.

---

Important: Branch Protection Update Required

In python-zk/kazoo repository settings, the master branch protection rule currently has Hound listed under required_status_checks:

• Repository maintainers/admins will need to remove Hound from the required status checks in branch protection settings (and optionally require Code Validation instead).
• Otherwise, future PRs will be blocked waiting for a Hound status check that no longer runs.

---

Key Changes

• HoundCI Retirement & Reviewdog Integration:
  • Removed .hound.yml and .flake8.
  • Added Reviewdog step via reviewdog/action-setup@v1 to .github/workflows/testing.yml using Ruff's native --output-format=rdjson with -reporter=github-pr-review and -filter-mode=added. This replicates HoundCI's inline commenting on PR diffs without external third-party bot flakiness.
• Ruff Migration & Configuration:
  • Replaced [tool.black] with [tool.ruff], [tool.ruff.lint], and [tool.ruff.format] in pyproject.toml.
  • Configured Ruff lint rules (select = ["E", "F", "W"], builtins = ["_"], matching ignores E203, E721, F401, F811, F821) and line-length = 79 to maintain consistency with existing Flake8 and Black rules.
  • Set target-version = "py39".
  • Pinned Ruff to ruff==0.16.7 in [dependency-groups] and dropped unused black and pep8 groups.
• Tox & CI Environments:
  • Added unified [testenv:ruff] in tox.ini running both ruff check and ruff format --check.
  • Preserved [testenv:pep8] and [testenv:black] for local developer workflows with deprecation notices pointing developers to the ruff environment.
  • Updated CI in .github/workflows/testing.yml to run TOX_VENV: ruff,mypy (one lint/format virtualenv instead of two).
• Formatting Consistency & Git Blame Preservation:
  • Formatted 12 files where Ruff's AST formatter slightly differed from Black (multiline implicit string joining and trailing comments on call arguments).
  • Added the reformat commit hash to .git-blame-ignore-revs under # Reformat using ruff 0.16.7 to preserve git blame history.

Verification

• tox -e ruff,mypy: All checks pass cleanly (62 files formatted, 0 lint violations, 0 typing issues).
• tox -e pep8 and tox -e black: Display deprecation notices and pass.

[codecov]

Codecov Report

❌ Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 94.96%. Comparing base (79cae1f) to head (8759aee).
⚠️ Report is 10 commits behind head on master.

Files with missing lines	Patch %	Lines
kazoo/client.py	75.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #813   +/-   ##
=======================================
  Coverage   94.96%   94.96%           
=======================================
  Files          27       27           
  Lines        3811     3811           
=======================================
  Hits         3619     3619           
  Misses        192      192           

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[ThosRTanner]

FIxes #774 I think