refactor: replace periodic tasks loop with background service

Foxnouns.Backend/Services/PeriodicTasksService.cs

@@ -0,0 +1,26 @@
+namespace Foxnouns.Backend.Services;
+
+public class PeriodicTasksService(ILogger logger, IServiceProvider services) : BackgroundService
+{
+    private readonly ILogger _logger = logger.ForContext<PeriodicTasksService>();
+
+    protected override async Task ExecuteAsync(CancellationToken ct)
+    {
+        using var timer = new PeriodicTimer(TimeSpan.FromMinutes(1));
+        while (await timer.WaitForNextTickAsync(ct))
+        {
+            _logger.Debug("Collecting metrics");
+            await RunPeriodicTasksAsync(ct);
+        }
+    }
+
+    private async Task RunPeriodicTasksAsync(CancellationToken ct)
+    {
+        _logger.Debug("Running periodic tasks");
+        
+        await using var scope = services.CreateAsyncScope();
+
+        var keyCacheSvc = scope.ServiceProvider.GetRequiredService<KeyCacheService>();
+        await keyCacheSvc.DeleteExpiredKeysAsync(ct);
+    }
+}