Mutex for actualize script (#5235)

* Simplify extension method
One parameter was not used

Furthermore, that unused parameter was preventing simpler calls (i.e. without a dedicated extension class). Now it is possible to register a call back with a lamda:

```php
Minz_ExtensionManager::addHook('feed_before_actualize', function () {
	// Hello
});
```

* Mutex for actualize script
In the case of extremely long cron jobs that are refreshing feeds, a cron job might start before the previous one has completed, leading to an accumulation of cron jobs running in parallel.
Although we already have a mutex preventing concurrency problems on a single feed refresh, the problem occurs in particular if each feed can take a long time (e.g. due to heavy processing, which is my usecase).
https://github.com/FreshRSS/FreshRSS/pull/5234 must be merged first

* Fiw wrong return

app/actualize_script.php

@@ -37,6 +37,30 @@ function notice(string $message): void {
 	}
 }
 
+// <Mutex>
+// Avoid having multiple actualization processes at the same time
+$mutexFile = TMP_PATH . '/actualize.freshrss.lock';
+$mutexTtl = 900; // seconds (refreshed before each new feed)
+if (file_exists($mutexFile) && ((time() - @filemtime($mutexFile)) > $mutexTtl)) {
+	unlink($mutexFile);
+}
+
+if (($handle = @fopen($mutexFile, 'x')) === false) {
+	notice('FreshRSS feeds actualization was already running, so aborting new run at ' . $begin_date->format('c'));
+	die();
+}
+fclose($handle);
+
+register_shutdown_function(function () use ($mutexFile) {
+	unlink($mutexFile);
+});
+
+Minz_ExtensionManager::addHook('feed_before_actualize', function ($feed) use ($mutexFile) {
+	touch($mutexFile);
+	return $feed;
+});
+// </Mutex>
+
 notice('FreshRSS starting feeds actualization at ' . $begin_date->format('c'));
 
 // make sure the PHP setup of the CLI environment is compatible with FreshRSS as well