Convert FirmwareEventArgs to a readonly struct

src/BizHawk.Client.Common/fwmanager/FirmwareEventArgs.cs

@@ -1,13 +1,22 @@
+#nullable enable
+
 using BizHawk.Emulation.Common;
 
 namespace BizHawk.Client.Common
 {
-	public sealed class FirmwareEventArgs
+	public readonly struct FirmwareEventArgs
 	{
-		public string Hash { get; set; }
+		public readonly string? Hash;
 
-		public FirmwareID ID { get; set; }
+		public readonly FirmwareID ID;
 
-		public long Size { get; set; }
+		public readonly long Size;
+
+		public FirmwareEventArgs(FirmwareID id, string? hash, long size)
+		{
+			Hash = hash;
+			ID = id;
+			Size = size;
+		}
 	}
 }

src/BizHawk.Client.Common/fwmanager/FirmwareManager.cs

@@ -42,14 +42,7 @@ namespace BizHawk.Client.Common
 			{
 				return null;
 			}
-
-			RecentlyServed.Add(new FirmwareEventArgs
-			{
-				ID = id,
-				Hash = resolved.Hash,
-				Size = resolved.Size
-			});
-
+			RecentlyServed.Add(new(id, resolved.Hash, resolved.Size));
 			return resolved.FilePath;
 		}