Fixed many warnings, moved some classes to their own files.

LightlessSync/Services/PairProcessing/PairProcessingLimiterSnapshot.cs

@@ -0,0 +1,9 @@
+using System.Runtime.InteropServices;
+
+namespace LightlessSync.Services.PairProcessing;
+
+[StructLayout(LayoutKind.Auto)]
+public readonly record struct PairProcessingLimiterSnapshot(bool IsEnabled, int Limit, int InFlight, int Waiting)
+{
+    public int Remaining => Math.Max(0, Limit - InFlight);
+}