feat: add config option "path" for file cache (#3297)

tests/CacheTest.php

@@ -0,0 +1,31 @@
+<?php
+
+namespace RssBridge\Tests;
+
+use PHPUnit\Framework\TestCase;
+
+class CacheTest extends TestCase
+{
+    public function testFileCache()
+    {
+        $temporaryFolder = sprintf('%s/rss_bridge_%s/', sys_get_temp_dir(), create_random_string());
+        mkdir($temporaryFolder);
+
+        $sut = new \FileCache([
+            'path' => $temporaryFolder,
+            'enable_purge' => true,
+        ]);
+        $sut->setScope('scope');
+        $sut->purgeCache(-1);
+        $sut->setKey(['key']);
+
+        $this->assertNull($sut->loadData());
+
+        $sut->saveData('data');
+        $this->assertSame('data', $sut->loadData());
+        $this->assertIsNumeric($sut->getTime());
+        $sut->purgeCache(-1);
+
+        // Intentionally not deleting the temp folder
+    }
+}