Grid Multi-Body: Resolve duplicate cell rendering and phantom nodes

Problem

With the new Grid Multi-Body architecture, cells (GridRow) were suffering from massive duplication, generating O(TotalColumns) DOM nodes for every row regardless of their assigned sub-grid container.

This occurred because src/grid/Row.mjs was retrieving its column configuration array (mountedColumns) correctly from its localized columnPositions, but indexed those positions directly into the global gridContainer.columns collection.

For instance, the bodyEnd sub-grid processing [0, 0] would query globalColumns.getAt(0), forcefully rendering the locked: 'start' activity field in its own body and triggering missing event listener target errors (target node not found: neo-sparkline-78__wrapper).

Solution

1. Rewired GridRow logic across all rendering passes (pooling and permanent cells) to safely extract the contextual dataField from the localized columnPositions.
2. Extracted the true column reference via columns.get(columnPosition.dataField) mapping.
3. This completely bounds column generation strictly to the explicit assignment rules for each respective sub-grid section (Start, Center, End).