Grid: Implement Main-Thread Addon Hover Synchronization

This is an architecture sub-task for Epic #9626.

Problem Description

The transition to a multi-body grid architecture means that a single logical row is now split across up to three physical grid bodies (Start, Center, End). Native SCSS :hover states only apply to the DOM nodes within a single grid body, resulting in disconnected highlighting when a user hovers over a segmented row.

To maintain perfect GPU scrolling performance and eliminate CSS bundle bloat, we need a hyper-optimized Main-Thread mechanism to synchronize these hover states.

Proposed Solution

Introduce the Neo.main.addon.GridRowHoverSync addon to systematically delegate native pointer events across multiple grid bodies with zero layout thrashing.

1. Native Hit-Testing: The Addon completely avoids computationally expensive mousemove coordination. It relies purely on the browser's native mouseover / mouseout event propagation. It perfectly complements pointer-events: none virtualization by letting the Browser GPU handle the lifecycle natively when a scroll buffer terminates.
2. relatedTarget Bailout: The Addon diffs the e.relatedTarget dynamically. If the pointer navigates within the boundaries of an identical data-record-id, it bypasses DOM mutations entirely, resulting in exactly zero unnecessary class toggles.
3. Dynamic Toggle Base: The Addon automatically unregisters itself via GridContainer.hasLockedColumns to ensure pristine 0-JS overhead when developers configure a traditional single-body Grid layout, gracefully defaulting to legacy SCSS native behavior.