Prevent invalid SaveData writes from damaging guest memory (#444)

Add an optional write monitor so the team can find future memory damage on each supported desktop system.

src/SharpEmu.Core/Memory/PhysicalVirtualMemory.cs

@@ -919,6 +919,7 @@ public sealed unsafe class PhysicalVirtualMemory : IVirtualMemory, IGuestMemoryA
                         Buffer.MemoryCopy(srcPtr, destPtr, (nuint)source.Length, (nuint)source.Length);
                     }
 
+                    NotifyGuestWriteWatch(virtualAddress, source);
                     return true;
                 }
             }
@@ -944,6 +945,14 @@ public sealed unsafe class PhysicalVirtualMemory : IVirtualMemory, IGuestMemoryA
         }
     }
 
+    private static void NotifyGuestWriteWatch(ulong virtualAddress, ReadOnlySpan<byte> source)
+    {
+        if (GuestWriteWatch.Armed)
+        {
+            GuestWriteWatch.Check(virtualAddress, source);
+        }
+    }
+
     private bool TryReadExclusive(ulong virtualAddress, Span<byte> destination)
     {
         var region = FindRegion(virtualAddress, (ulong)destination.Length);
@@ -1016,6 +1025,7 @@ public sealed unsafe class PhysicalVirtualMemory : IVirtualMemory, IGuestMemoryA
                     Buffer.MemoryCopy(srcPtr, destPtr, (nuint)source.Length, (nuint)source.Length);
                 }
 
+                NotifyGuestWriteWatch(virtualAddress, source);
                 return true;
             }
 
@@ -1040,6 +1050,7 @@ public sealed unsafe class PhysicalVirtualMemory : IVirtualMemory, IGuestMemoryA
                 }
             }
 
+            NotifyGuestWriteWatch(virtualAddress, source);
             return true;
         }