Fix duplicate joins when resolving multiple columns

Check query's existing joins instead of a local array, preventing
duplicate table joins when resolveColumnWithJoins is called multiple
times (e.g. for both groupBy and aggregate columns).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: SimonBarrettACT

src/ReportBuilder.php

@@ -61,7 +61,9 @@ protected function resolveColumnWithJoins(Builder $query, string $key): string
         $parts = explode('.', $key);
         $columnName = array_pop($parts);
         $currentModel = $query->getModel();
-        $joined = [];
+        $existingJoins = collect($query->getQuery()->joins ?? [])
+            ->pluck('table')
+            ->all();
 
         foreach ($parts as $relationName) {
             if (! method_exists($currentModel, $relationName)) {
@@ -71,7 +73,7 @@ protected function resolveColumnWithJoins(Builder $query, string $key): string
             $relation = $currentModel->{$relationName}();
             $relatedTable = $relation->getRelated()->getTable();
 
-            if (in_array($relatedTable, $joined, true)) {
+            if (in_array($relatedTable, $existingJoins, true)) {
                 $currentModel = $relation->getRelated();
 
                 continue;
@@ -93,7 +95,7 @@ protected function resolveColumnWithJoins(Builder $query, string $key): string
                 );
             }
 
-            $joined[] = $relatedTable;
+            $existingJoins[] = $relatedTable;
             $currentModel = $relation->getRelated();
         }