Revises the specification to reflect that EasyGrid<T> extends Grid<T> rather than wrapping it, and removes everything that is already inherited.

• Replace "wraps Grid" with "extends Grid" throughout
• Drop sections whose API is entirely inherited: Data Binding, Selection, Events, Filtering
• Strip EasyColumnConfig down to EasyGrid-specific methods only (type-aware formatting, rendering conveniences, export options);standard column properties are now set directly via getColumnByKey() or getColumn()
• Add withExportHeader / withExportable to EasyColumnConfig (previously mentioned in the Exporter section but missing from the class definition)
• Update all code examples accordingly
• Simplify the Serialization section to acknowledge Grid's existing support