DataGrid: Fix detail grid reloading data when collapsed master row reenters viewport with virtual row rendering (T1326188)

[Alyar666]

No description provided.

[Copilot]

Pull request overview

Fixes an issue where a DataGrid’s master-detail content could be re-created (and the detail grid’s data reloaded) when a collapsed master row re-enters the viewport under virtual row rendering.

Changes:

• Clear DataController’s processed-items cache after toggling master row expand/collapse state to prevent stale processed rows from being reused during subsequent viewport refreshes.
• Add a new TestCafe functional test covering the regression scenario (standard scrolling + rowRenderingMode: 'virtual').
• Fix TestCafe masterDetail visual test helper imports and correct the container page path.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
packages/devextreme/js/__internal/grids/grid_core/master_detail/m_master_detail.ts	Clears processed-items cache after row expand/collapse to avoid stale master-detail row processing during viewport refresh.
packages/devextreme/js/__internal/grids/grid_core/data_controller/m_data_controller.ts	Adds a small helper to reset _cachedProcessedItems.
e2e/testcafe-devextreme/tests/dataGrid/common/masterDetail/visual.ts	Fixes helper import paths and corrects the relative container.html path for the fixture.
e2e/testcafe-devextreme/tests/dataGrid/common/masterDetail/functional.ts	Adds a regression test ensuring the detail grid does not reload when a collapsed master row re-enters the viewport.