create merge clover coverage command

src/Clover/Dto/Accumulator.php

@@ -0,0 +1,41 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Dannecron\CoverageMerger\Clover\Dto;
+
+class Accumulator
+{
+    /** @var array<string, FileDto> $files */
+    private array $files;
+
+    public function __construct()
+    {
+        $this->files = [];
+    }
+
+    /**
+     * @return array<string, FileDto>
+     */
+    public function getFiles(): array
+    {
+        return $this->files;
+    }
+
+    public function addFile(string $fileName, FileDto $file): self
+    {
+        /** @var FileDto|null $existedFile */
+        $existedFile = $this->getFiles()[$fileName] ?? null;
+
+        if ($existedFile !== null) {
+            $existedFile->mergeFile($file);
+
+            return $this;
+        }
+
+        $merged = \array_merge($this->files, [$fileName => $file]);
+        $this->files = $merged;
+
+        return $this;
+    }
+}