Problem:
Currently, Neo.mjs grid header buttons use tri-state sorting (ASC, DESC, null). This was originally designed to allow reverting to an unsorted state and testing collection.allItems. However, for most real-world use cases (like the DevIndex grid), a two-state sorting mechanism (ASC, DESC) is more intuitive and expected by users.

Proposed Solution:
Introduce a new reactive configuration, useTriStateSorting_, on grid components. This config should default to false (enabling two-state sorting by default) and propagate from the GridContainer down to the HeaderToolbar and finally to the individual HeaderButtons.

• src/grid/header/Button.mjs: Add useTriStateSorting_: false and update onClick to bypass the null state based on this config.
• src/grid/header/Toolbar.mjs: Add useTriStateSorting_: false to propagate the setting to its child buttons and respond to dynamic changes.
• src/grid/Container.mjs: Expose useTriStateSorting_: false to provide a top-level developer API to configure sorting behavior for the entire grid.