many fixes and improvements - rework for modules/ and common/

feat(emailer): add Postmark and Resend providers

backend/Modules/Creators/Services/CreatorLookup.cs

@@ -0,0 +1,26 @@
+using Hutopy.Modules.Creators.Contracts;
+using Hutopy.Modules.Creators.Data;
+
+namespace Hutopy.Modules.Creators.Services;
+
+public sealed class CreatorLookup(
+    CreatorsDbContext context)
+    : ICreatorLookup
+{
+    public async Task<CreatorReference?> GetCreatorAsync(Guid creatorId, CancellationToken cancellationToken)
+    {
+        Creator? creator = await context
+            .Creators
+            .FirstOrDefaultAsync(c => c.Id == creatorId, cancellationToken);
+
+        return creator is null
+            ? null
+            : new CreatorReference(
+                creator.Id,
+                creator.Name,
+                creator.PortraitUrl,
+                creator.IsStripeDetailsSubmitted,
+                creator.IsStripeChargesEnabled,
+                creator.StripeAccountId);
+    }
+}

backend/Modules/Creators/Services/SlugPurger.cs

@@ -0,0 +1,43 @@
+using Hutopy.Modules.Creators.Data;
+
+namespace Hutopy.Modules.Creators.Services;
+
+public class SlugPurger(CreatorsDbContext context)
+{
+    private static readonly SemaphoreSlim Semaphore = new(1, 1);
+    private static DateTimeOffset s_lastPurgeTime = DateTimeOffset.MinValue;
+    private static readonly TimeSpan MinTimeBetweenPurges = TimeSpan.FromSeconds(10);
+
+    public async Task PurgeExpiredSlugsAsync(CancellationToken ct)
+    {
+        // Try to acquire the semaphore
+        if (!await Semaphore.WaitAsync(0, ct))
+        {
+            // Another purge operation is in progress, skip this one
+            return;
+        }
+
+        try
+        {
+            var now = DateTimeOffset.UtcNow;
+            if (now - s_lastPurgeTime < MinTimeBetweenPurges)
+            {
+                // Not enough time has passed since the last purge
+                return;
+            }
+
+            // Delete expired slugs that are not in use
+            await context
+                .Slugs
+                .Where(s => s.ReservedUntil < now && s.UsedBy == null)
+                .ExecuteDeleteAsync(ct);
+
+            // Update the last purge time regardless of whether we found expired slugs or not
+            s_lastPurgeTime = now;
+        }
+        finally
+        {
+            Semaphore.Release();
+        }
+    }
+}