feat: Add #[CollectedBy] attribute

[binaryfire]

This PR ports Laravel's #[CollectedBy] attribute to Hypervel, allowing models to declaratively specify a custom collection class.

Summary

• Adds #[CollectedBy] attribute for declaring custom collection classes on models
• Adds HasCollection trait providing the newCollection() method with attribute resolution
• Modifies Model to use the new HasCollection trait

Usage

use Hypervel\Database\Eloquent\Attributes\CollectedBy;
use Hypervel\Database\Eloquent\Model;

#[CollectedBy(CustomUserCollection::class)]
class User extends Model
{
    // ...
}

// Now User::all() returns a CustomUserCollection
$users = User::all(); // instanceof CustomUserCollection

Changes

New Files

• src/core/src/Database/Eloquent/Attributes/CollectedBy.php - The attribute class
• src/core/src/Database/Eloquent/Concerns/HasCollection.php - Trait providing newCollection() with attribute resolution
• tests/Core/Database/Eloquent/Concerns/HasCollectionTest.php - Tests (9 tests, 16 assertions)

Modified Files

• src/core/src/Database/Eloquent/Model.php - Added HasCollection trait, removed inline newCollection() method

How It Works

1. When newCollection() is called on a model, the HasCollection trait checks for a #[CollectedBy] attribute
2. If found, the specified collection class is used
3. If not found, falls back to the default Hypervel\Database\Eloquent\Collection
4. Collection classes are cached per model class for performance

Notes

• PHP attributes are not inherited - child classes need their own #[CollectedBy] attribute if they want a custom collection
• This follows Laravel's implementation pattern

[binaryfire]

@albertcht I've also added HasCollection support to Pivot and MorphPivot to match Laravel's behavior.

Since Hypervel's pivot classes extend Hyperf's base classes (not Hypervel's Model), they don't inherit collection functionality automatically. I've added the HasCollection trait and $collectionClass property to both classes.

This required changing Collection's template constraint from TModel of \Hypervel\...\Model to TModel of \Hyperf\...\Model so it works with any Hyperf-based model. This is correct since Hypervel's Collection extends Hyperf's Collection anyway.