EuiDataGridColumnResizer handles column resize drag interactions within EuiDataGrid.

• File: components/datagrid/body/header/column_resizer.tsx
• Class size: 80 lines
• State: initialX, offset
• Lifecycle: None

Migration notes:

State-only, no lifecycle. Drag handling via mouse events. State maps to useState, event handlers stay as functions.

Acceptance criteria:

• Convert to function component with useState
• Maintain drag resize behavior
• All existing tests pass
• Verify no performance regressions in DataGrid column resizing