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 embedded server is a .NET app).
• pip install -e . → black --check . → fetch the bundled server → python -m unittest discover -s tests.
• The server is fetched via the project's own setup.py sdist hook (populates ravendb_embedded/target/nuget). setuptools/wheel are installed explicitly since modern virtualenvs no longer ship them.
• pyproject.toml pins black line-length to 120 (matches the ravendb-python-client repo).

Test fixes (required for the suite to be green in CI)

The suite previously assumed a developer machine. Minimal fixes:

• test_runtime_framework_version_matcher.test_match_1 — was asserting the default framework_version contains +, but the default is now empty (commit "Don't enforce framework version"). Updated to assert the current "unenforced" contract. Resolution logic stays covered by test_match_2/3/4.
• test_custom_provider — the zip/directory external-server tests depended on the current working directory and a pre-built ravendb-server.zip. Now they build the zip from the bundled server and use an absolute path, so they run anywhere.
• test_secured_basic — hardcodes local Windows HTTPS cert paths; now skipUnless those certs exist (still runs on a dev machine, skips in CI).

Verified locally

Ran the exact CI steps in a clean venv (Python 3.12 + .NET 8): 9 tests OK (1 skipped — secured).

No RAVEN_LICENSE needed — the embedded server runs community edition for these tests.