Improve return phpdoc for static analysis and completion

Author: GromNaN

src/Eloquent/Builder.php

@@ -54,6 +54,11 @@ class Builder extends EloquentBuilder
         'tomql',
     ];
 
+    /**
+     * @return ($function === null ? PipelineBuilder : self)
+     *
+     * @inheritdoc
+     */
     public function aggregate($function = null, $columns = ['*'])
     {
         $result = $this->toBase()->aggregate($function, $columns);

src/Eloquent/Model.php

@@ -49,6 +49,7 @@
 use function uniqid;
 use function var_export;
 
+/** @mixin Builder */
 abstract class Model extends BaseModel
 {
     use HybridRelations;