Refactor bulk info provider: replace complex arrays with DTOs

- Add BulkSearchResponseDTO, FieldMappingDTO for type safety
- Use composition instead of inheritance in BulkSearchResultDTO
- Remove unnecessary BulkSearchRequestDTO
- Fix N+1 queries and API error handling
- Fix Add Mapping button functionality

src/Services/InfoProviderSystem/DTOs/PartSearchResultDTO.php

@@ -0,0 +1,114 @@
+<?php
+/*
+ * This file is part of Part-DB (https://github.com/Part-DB/Part-DB-symfony).
+ *
+ *  Copyright (C) 2019 - 2023 Jan Böhmer (https://github.com/jbtronics)
+ *
+ *  This program is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU Affero General Public License as published
+ *  by the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  This program is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU Affero General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Affero General Public License
+ *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+declare(strict_types=1);
+
+namespace App\Services\InfoProviderSystem\DTOs;
+
+use App\Entity\Parts\Part;
+
+/**
+ * Represents the search results for a single part from bulk info provider search.
+ * This DTO provides type safety and clear structure for part search results.
+ */
+readonly class PartSearchResultDTO
+{
+    /**
+     * @param Part $part The part that was searched for
+     * @param SearchResultWithMetadataDTO[] $searchResults Array of search results found for this part
+     * @param string[] $errors Array of error messages encountered during search
+     */
+    public function __construct(
+        public Part $part,
+        public array $searchResults = [],
+        public array $errors = []
+    ) {}
+
+    /**
+     * Create from legacy array format for backwards compatibility.
+     * @param array{part: Part, search_results: array, errors: string[]} $data
+     */
+    public static function fromArray(array $data): self
+    {
+        $searchResults = [];
+        foreach ($data['search_results'] as $result) {
+            $searchResults[] = SearchResultWithMetadataDTO::fromArray($result);
+        }
+
+        return new self(
+            part: $data['part'],
+            searchResults: $searchResults,
+            errors: $data['errors'] ?? []
+        );
+    }
+
+    /**
+     * Convert to legacy array format for backwards compatibility.
+     * @return array{part: Part, search_results: array, errors: string[]}
+     */
+    public function toArray(): array
+    {
+        $searchResults = [];
+        foreach ($this->searchResults as $result) {
+            $searchResults[] = $result->toArray();
+        }
+
+        return [
+            'part' => $this->part,
+            'search_results' => $searchResults,
+            'errors' => $this->errors,
+        ];
+    }
+
+    /**
+     * Check if this part has any search results.
+     */
+    public function hasResults(): bool
+    {
+        return !empty($this->searchResults);
+    }
+
+    /**
+     * Check if this part has any errors.
+     */
+    public function hasErrors(): bool
+    {
+        return !empty($this->errors);
+    }
+
+    /**
+     * Get the number of search results for this part.
+     */
+    public function getResultCount(): int
+    {
+        return count($this->searchResults);
+    }
+
+    /**
+     * Get search results sorted by priority (ascending).
+     * @return SearchResultWithMetadataDTO[]
+     */
+    public function getResultsSortedByPriority(): array
+    {
+        $results = $this->searchResults;
+        usort($results, fn($a, $b) => $a->getPriority() <=> $b->getPriority());
+        return $results;
+    }
+}