Migrate dev tooling from pip-tools/tox to uv

[hf-krechan]

Summary

• Move dev-tool extras (tests, coverage, linting, type_check, spellcheck, formatting) from [project.optional-dependencies] to PEP 735 [dependency-groups] in pyproject.toml, plus a dev group bundling them for local setup (mirroring the old tox dev env, minus packaging tooling).
• Drop the test_packaging group (build/twine) entirely — uv build and uv publish --dry-run replace them natively with no dependency group needed.
• Remove tox.ini, requirements.txt, requirements.in; add uv.lock (generated via uv lock).
• Set [tool.uv] default-groups = [] so a bare uv sync/uv run doesn't silently pull in the dev group.
• Rewrite all .github/workflows/*.yml to use astral-sh/setup-uv@v9.0.0 + uv sync --group <x> + uv run --group <x> <tool> instead of pip install tox + tox -e <x>; packaging_test.yml and the publish job now call uv build/uv publish --dry-run directly.
• Update .github/dependabot.yml ecosystem from pip to uv.
• Bump stale black (22.10.0 → 26.5.1), isort (5.10.1 → 8.0.1), and pre-commit-hooks (v4.3.0 → v6.0.0) pins in .pre-commit-config.yaml to match the versions now pinned in pyproject.toml / support current Python, and add the astral-sh/uv-pre-commit uv-lock hook.
• Fix a stale .gitignore template placeholder (src/_your_package_version.py → src/_generics_version.py) and a codespell false positive on uv.lock (added [tool.codespell] skip = "uv.lock").

Job names/matrix keys for pytest, check_packaging, black (black)/black (isort), and Python Code Quality and Lint (linting)/(type_check) were kept identical to what's currently pinned in the repo's branch protection ruleset's required status checks.

Test plan

• uv lock / uv sync --group dev succeed, project installs in editable mode
• uv run pytest — 27 passed
• Per-group isolated syncs (UV_PROJECT_ENVIRONMENT=<scratch> uv sync --group X) for linting, type_check, coverage, formatting, spellcheck — all pass with expected tool output
• uv build + uv publish --dry-run dist/* succeed
• pre-commit run --all-files — all hooks pass (uv-lock, check-yaml, end-of-file-fixer, trailing-whitespace, black, isort)
• grep -rnE "setup-uv@v[0-9]+$" .github/workflows/ returns nothing (no floating-major tags)
• CI on this PR (not required before opening per task instructions)

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