chore: Migrate from Poetry to uv for dependency management

[jsonbailey]

Summary

The 1.6.0 release publish failed because release-please.yml installed Poetry via actions-poetry with the default poetry-version: latest, and current Poetry requires Python 3.10+ while the release job ran on Python 3.9 (dataclass() got an unexpected keyword argument 'slots'). Rather than pin Poetry, this migrates the repo from Poetry to uv, matching launchdarkly/python-server-sdk#431.

It also adds Python 3.14 to the test matrix and supported classifiers.

Note: the v1.6.0 tag and GitHub release already exist; only the PyPI publish failed (PyPI is still at 1.5.1). Once this merges, 1.6.0 can be published via the Publish Package workflow (manual-publish.yml).

What changed

pyproject.toml

• Converted [tool.poetry] → standard PEP 621 [project]
• [tool.poetry.extras] async → [project.optional-dependencies]
• Dev / contract-tests / docs groups → [dependency-groups]
• Build backend poetry-core → hatchling, with the wheel scoped to ld_eventsource and excluding ld_eventsource/testing (preserving Poetry's behavior)
• Preserved requires-python = ">=3.9" and all version constraints
• Added a mypy override so it does not parse third-party pytest internals (their source uses match syntax newer than the project's 3.9 floor)
• Added the Python :: 3.14 classifier

CI / release workflows

• ci.yml, manual-publish.yml, release-please.yml, manual-publish-docs.yml: replaced actions/setup-python + abatilo/actions-poetry with astral-sh/setup-uv (pinned to v8.2.0)
• Release/publish workflows run on Python 3.10 (off the EOL 3.9); CI matrix runs 3.9–3.14
• .github/actions/build/action.yml: poetry build → uv build --out-dir dist

Other

• Makefile: poetry install/run → uv sync / uv run
• CONTRIBUTING.md: setup instructions use uv sync
• .readthedocs.yml: uv-based environment
• .gitignore: drop poetry.lock; ignore uv.lock and .venv/ (library — lockfile not committed)

Test plan

Verified locally:

• uv sync --all-extras resolves and installs cleanly
• uv build produces sdist + wheel; ld_eventsource/testing excluded from the wheel, retained in the sdist
• make test — 124 passed (also verified on Python 3.14)
• make lint — mypy / isort / pycodestyle all pass
• make docs — builds cleanly under uv

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