refactor: use DTO and terminate middleware for better performance

- Add PageviewData readonly DTO class for type safety
- Update AnalyticsClient to accept PageviewData instead of array
- Move analytics sending to terminate() method (runs after response sent)
- Update all tests for new DTO pattern

src/Data/PageviewData.php

@@ -0,0 +1,30 @@
+<?php
+
+namespace Mattitja\Analytics\Data;
+
+readonly class PageviewData
+{
+    public function __construct(
+        public string $siteKey,
+        public string $url,
+        public string $ip,
+        public string $userAgent,
+        public ?string $referrer = null,
+    ) {}
+
+    public function toArray(): array
+    {
+        $data = [
+            'k' => $this->siteKey,
+            'u' => $this->url,
+            'ip' => $this->ip,
+            'ua' => $this->userAgent,
+        ];
+
+        if ($this->referrer !== null && $this->referrer !== '') {
+            $data['r'] = $this->referrer;
+        }
+
+        return $data;
+    }
+}