Use uv as the default test environment

[splasky]

Summary

• Move package metadata, runtime dependencies, dev dependencies, and pytest configuration into pyproject.toml.
• Track uv.lock and remove duplicated dependency/config files: requirements.txt and pytest.ini.
• Update README and GitHub Actions to use uv sync --locked and uv run pytest.
• Start the Datastore emulator with --consistency=1.0 so emulator-backed tests are deterministic.

Validation

• uv sync --locked passed after rebasing onto origin/main.
• GCLOUD_PATH=/mnt/workspace/code/google-cloud-sdk/bin/gcloud uv run pytest -> 399 passed.
• Superset master datastore engine spec tests: SUPERSET_CONFIG=tests.integration_tests.superset_test_config SUPERSET_TESTENV=true .venv/bin/pytest -vv tests/integration_tests/db_engine_specs/datastore_tests.py -> 20 passed.
• Superset 6.0.0: Apache upstream tag 6.0.0 was checked locally, but that source tree does not contain tests/integration_tests/db_engine_specs/datastore_tests.py, DatastoreDbEngineSpec, or sqlalchemy_datastore references, so the same Superset datastore test module is not available on that tag. The package itself was importable in the Superset 6.0.0 environment.

Notes

uv.lock is intentionally tracked so CI and local development resolve the same dependency set when using uv sync --locked.