[two_dimensional_scrollables] Fix merged cells unmerging behind pinned spans

[Piinks]

This PR addresses an issue where merged cells in a TableView would "unmerge" or break when the first cell of the merge was scrolled into the area overlaid by a pinned row or column.

• Updated RenderTableViewport to expand the _targetLeadingColumnPixel and _targetLeadingRowPixel calculation to include the pinned extent.
• Strengthened the documentation in TableView and TableViewCell to explicitly state that the same child and merge information must be returned from every vicinity in the merge to avoid unmerging when cells are culled due to lazy loading.

Fixes flutter/flutter#174862

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[gemini-code-assist]

Code Review

This pull request updates the two_dimensional_scrollables package to version 0.4.2, addressing an issue where merged cells would unmerge when the primary cell was overlaid by a pinned row or column. The fix modifies RenderTableViewport to include pinned row and column extents when calculating the leading layout pixels. Documentation for TableView and TableViewCell has been updated to clarify that consistent merge information must be returned for all vicinities within a merged cell, and new regression tests have been added to verify the behavior. I have no feedback to provide.

[AbdeMohlbi]

Code Review

This pull request updates the two_dimensional_scrollables package to version 0.4.2, addressing an issue where merged cells would unmerge when the primary cell was overlaid by a pinned row or column. The fix modifies RenderTableViewport to include pinned row and column extents when calculating the leading layout pixels. Documentation for TableView and TableViewCell has been updated to clarify that consistent merge information must be returned for all vicinities within a merged cell, and new regression tests have been added to verify the behavior. I have no feedback to provide.

that's new, usually you always seem to have a comment about any change, should we go to a doctor 🫠​?