Grid Multi-Body: SubGrid Row Pooling & Vertical Sync Refactoring

Phase 3 of the Multi-Body Epic (#9486).

Currently, Neo.grid.Body assumes it is the sole render target for the grid, handling its own full store range calculations and scrollManager events.

In the Multi-Body architecture, the Body component must become a "SubGrid".

Requirements:

1. Vertical Sync Overhaul:

• The actual vertical scrollTop value comes from the outer wrapper (neo-grid-body-wrapper).
• The ScrollManager must be updated to listen to this wrapper, not the individual bodies.
• When a vertical scroll occurs, the ScrollManager (or a central BodyManager inside Container) must calculate the startIndex and endIndex of the visible rows once.

2. Synchronized Rendering (createViewData):

• The three SubGrids (start, center, end) must not calculate their own startIndex/endIndex.
• They must receive the exact same index range from the orchestrator.
• All active SubGrids must execute their row pooling loops synchronously, mapping the same recordId to the same physical pool index, ensuring they receive the identical translateY offset to stay vertically aligned.

3. Component Refactoring (Isolated Pooling):

• Strip out the logic in grid.Body that currently assumes it owns the vertical scrollbar.
• Expose setter methods or configs that allow the parent Container to drive the createViewData cycle externally for all active bodies simultaneously.
• Each SubGrid must manage its own pool of Row instances based exclusively on its specific column collection (Left, Center, or Right).