Implement a Proxy set trap for Neo.state.Provider data to enable direct reactive assignments

Description The Neo.state.Provider currently requires the use of setData() to trigger reactivity when updating data properties. To enhance developer experience and align with more intuitive JavaScript patterns, we should implement a Proxy set trap on the stateProvider.data object. This will allow direct assignments (e.g., stateProvider.data.myProperty = 'newValue') to automatically trigger the underlying setData() mechanism, ensuring reactivity.

Problem Developers accustomed to direct property assignments for state management in other reactive frameworks may find the explicit setData() calls cumbersome or non-idiomatic. This can lead to confusion and potential bugs if setData() is not used, as direct assignments currently do not trigger the Effect system.

Proposed Solution Modify src/state/createHierarchicalDataProxy.mjs to include a set trap within the Proxy returned by createHierarchicalDataProxy.

The set trap should:

1. Intercept direct assignments to properties on the stateProvider.data proxy.
2. Determine the correct Neo.state.Provider instance (current or a parent in the hierarchy) that "owns" the property being assigned. This can be achieved by leveraging the existing getOwnerOfDataProperty method.
3. Call the setData() method on the identified owning StateProvider with the fullPath of the property and the new value. This will ensure that the Neo.core.Config instances are updated and the Effect system is triggered, maintaining full reactivity.

Benefits

• Improved developer ergonomics: Allows for more natural and concise data updates.
• Reduced boilerplate: Eliminates the need for explicit setData() calls in many common scenarios.
• Enhanced consistency: Aligns the StateProvider's data manipulation with common reactive programming paradigms.

Acceptance Criteria

• Direct assignments to stateProvider.data.someProperty (including nested properties like stateProvider.data.user.firstName) successfully trigger reactive updates in bound components.
• The onDataPropertyChange method in Neo.state.Provider is correctly invoked when data is updated via direct assignment.
• Existing setData() calls continue to function as expected.
• No regressions are introduced in the StateProvider's reactivity or hierarchical data access.
• Comprehensive unit tests are added to test/siesta/tests/state/Provider.mjs to cover direct assignment scenarios, including nested properties and various data types.