Add CI (tests + black) for v7.2

[poissoncorp]

Adds a GitHub Actions workflow that runs the test suite (and a black format check) on push / PR to v7.2, across Python 3.9–3.13.

CI (.github/workflows/tests.yml)

• setup-python (matrix 3.9–3.13) + setup-dotnet 8.0 (the test driver runs the embedded RavenDB server, a .NET app).
• pip install -e . → black --check . → python -m unittest discover -s tests.
• No server-fetch step needed: the server binaries ship inside the ravendb-embedded dependency wheel.
• pyproject.toml pins black line-length to 120 (matches the ravendb-python-client repo).

Verified locally

Ran the exact CI steps in a clean venv (Python 3.12 + .NET 8, pulling ravendb-embedded from PyPI): 3 tests OK. No test changes were needed — the suite was already clean. No RAVEN_LICENSE required (community edition).