[Observable] should be tested with semi-automatic properties in C# 14

The [Observable] aspect has not been tested with C# 14 semi-automatic properties using the field keyword.

Background

C# 14 introduces semi-automatic properties that use the field keyword to access an auto-generated backing field:

public string Name
{
    get => field;
    set => field = value?.Trim() ?? throw new ArgumentNullException();
}

Required Testing

The [Observable] aspect in Metalama.Patterns.Observability needs testing with:

1. Semi-automatic properties using field keyword
2. Dependency analysis of properties using field
3. Change notification generation for field-backed properties
4. Computed properties that depend on semi-automatic properties

Acceptance Criteria

• [ ] Add aspect tests for semi-automatic properties
• [ ] Verify PropertyChanged events are raised correctly
• [ ] Verify dependency tracking works for computed properties depending on semi-automatic properties
• [ ] Document any limitations or special behaviors