Reuse a shared SQL Server container for integration tests #1325

Goal

Reduce integration-test startup time by creating one SQL Server Testcontainers instance per test run or shared fixture instead of starting a new SQL Server container for every scenario.

Scope

• Introduce a shared SQL Server fixture/lifecycle for the integration-test project.
• Keep SQL Server startup and health checking at fixture/run scope.
• Use unique database names, schemas, or reliable reset logic so scenarios remain isolated.
• Ensure dependent containers use the shared SQL Server connection details and mapped host port.
• Keep cleanup deterministic and compatible with the existing shared-service handling.
• Consider Testcontainers reuse only after fixture sharing is in place; if enabled, use a stable container identity/label and document cleanup expectations.

Acceptance criteria

• SQL Server starts at most once for the relevant integration-test run.
• Scenarios can run without leaking rows, schemas, or migrations into one another.
• SQL Server is cleaned up when the fixture/test run completes, including failure paths.
• Parallel execution behavior is documented or explicitly prevented where shared state makes it unsafe.
• Capture before/after startup timing for the integration-test suite.