Upgrade bUnit to v2 and complete the test context migration

[Copilot]

The test suite was still on bUnit 1.x and relied on APIs that are obsolete in bUnit 2.x. This updates the suite to the current bUnit surface and finishes the migration by replacing the hidden DisposeAsync() shim with a proper async disposal pattern in the shared test context.

• Dependency update

  • Bumped bunit from 1.40.0 to 2.7.2

• bUnit API migration

  • Swapped TestContext usage to BunitContext
  • Replaced obsolete RenderComponent<T>() calls with canonical Render<T>()
  • Updated component disposal in tests to the v2 async model

• Shared test context cleanup

  • Removed the hidden public new DisposeAsync()
  • Implemented IAsyncLifetime.DisposeAsync() explicitly
  • Moved local teardown into a protected virtual helper so derived test contexts can extend disposal without shadowing bUnit lifecycle members
  • Kept SQLite connection cleanup and bUnit context disposal in one path

• Test alignment

  • Adjusted a small set of test expectations/fixtures to match current import flow behavior and keep the suite deterministic under the migrated setup

public abstract class JaTestContext : BunitContext, IAsyncLifetime
{
    Task IAsyncLifetime.DisposeAsync() => DisposeTestContextAsync();

    protected virtual async Task DisposeTestContextAsync()
    {
        if (_dbConnection != null)
        {
            await _dbConnection.CloseAsync();
            await _dbConnection.DisposeAsync();
            _dbConnection = null;
        }

        await base.DisposeAsync();
    }
}