feat: Add #[ObservedBy] attribute support

[binaryfire]

This PR adds Laravel-style #[ObservedBy] attribute support to Hypervel, allowing observers to be declared directly on model classes.

Features

#[ObservedBy] Attribute

Declare observers directly on your models:

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

#[ObservedBy(UserObserver::class)]
class User extends Model {}

// Multiple observers via array
#[ObservedBy([AuditObserver::class, CacheObserver::class])]
class Post extends Model {}

// Or multiple attributes (repeatable)
#[ObservedBy(AuditObserver::class)]
#[ObservedBy(CacheObserver::class)]
class Comment extends Model {}

Inheritance Support

Observers declared on parent classes are automatically inherited by children:

#[ObservedBy(AuditObserver::class)]
abstract class BaseModel extends Model {}

#[ObservedBy(UserObserver::class)]
class User extends BaseModel {}
// User gets both AuditObserver and UserObserver

Pivot Model Support

This PR also adds observer support to Pivot and MorphPivot models, similar to laravel. This was previously missing in Hypervel:

#[ObservedBy(RoleUserObserver::class)]
class RoleUser extends Pivot {}

// Service provider registration now works too
RoleUser::observe(RoleUserObserver::class);

Changes

New Files

• src/core/src/Database/Eloquent/Attributes/ObservedBy.php - The attribute class
• tests/Core/Database/Eloquent/Concerns/HasObserversTest.php - Tests (13 tests, 16 assertions)

Modified Files

• src/core/src/Database/Eloquent/Concerns/HasObservers.php - Added bootHasObservers() and resolveObserveAttributes()
• src/core/src/Database/Eloquent/Relations/Pivot.php - Added HasObservers trait
• src/core/src/Database/Eloquent/Relations/MorphPivot.php - Added HasObservers trait

Implementation Notes

Laravel puts observer functionality in HasEvents, but Hypervel already has a separate HasObservers trait. This PR extends that existing pattern.

For pivot models, Laravel's Pivot extends Model directly, so it inherits observer support automatically. Hypervel's Pivot extends Hyperf's Pivot (which extends Hyperf's Model), so we add the HasObservers trait directly to Pivot and MorphPivot to achieve the same result.

Testing

All tests pass:

• HasObserversTest - 13 tests covering attribute resolution, inheritance, and pivot support
• ObserverManagerTest - Existing tests still pass
• ModelListenerTest - Existing tests still pass