Raise a typed terminal timeout instead of returning None from workflow result

[rmcdaniel]

Confirmed against main fe4b059 with AsyncMock describe/history responses, no runtime or credentials: status=failed plus a persisted WorkflowTimedOut event causes Client.get_result to return None. A real deadline is therefore indistinguishable from successful None output. Found during the timeout parity review for sdk-php#55; Rust already maps this terminal outcome explicitly.

Acceptance:

• Raise an exported WorkflowTimedOut SDK exception for WorkflowTimedOut history (execution_timeout and run_timeout).
• Keep the caller's polling TimeoutError distinct and unchanged.
• Preserve the selected run used to retrieve history and existing success/failure/cancellation/termination behavior.
• Add focused red/green tests and run Ruff, mypy and the unit suite.

This is a result-mapping correction, not a replay or wire-protocol change. Do not introduce transport compatibility for old prereleases.

[rmcdaniel]

Fixed in #55 and prepared for release in #56. Both PRs passed the complete public CI matrix, including real Server integration. The immutable 2.0.2 tag points to 841bf7e; the existing protected PyPI workflow is now responsible for publishing and verifying that exact artifact.

[rmcdaniel]

Released as Python SDK 2.0.2. The protected publication workflow completed successfully: https://github.com/durable-workflow/sdk-python/actions/runs/34020903535 . It verified built metadata, installed and smoke-tested the package, published to PyPI, verified exact registry metadata and supported installs, and created the GitHub Release. PyPI exposes the non-yanked 2.0.2 wheel and source archive. The rendered PyPI page challenge is advisory; exact registry JSON verification passed.