feat: remove irrelevant withConfig and withModel methods

[moreirawebmaster]

This PR removes the withConfig() and withModel() methods from EngineHttpTracking as they were deemed irrelevant for the new architecture.

Changes Made

• BREAKING: Removed EngineHttpTracking.withConfig() method
• BREAKING: Removed EngineHttpTracking.withModel() method
• Updated CHANGELOG.md to document the breaking changes
• Updated migration guide with information about removed methods
• Removed related tests for the removed methods
• Updated example code to use updateModel() instead

Migration

For runtime configuration changes, use updateModel() instead:

```dart
// Instead of withConfig() or withModel()
EngineHttpTracking.updateModel(newModel);
// Perform operations...
// Restore original model if needed
EngineHttpTracking.updateModel(originalModel);
```

Testing

• ✅ All existing tests pass
• ✅ Removed tests for deprecated methods
• ✅ Example app updated and working

Type of Change

• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes"