Provide some base implementations on `Watch`

src/BizHawk.Client.Common/tools/Watch/ByteWatch.cs

@@ -99,10 +99,6 @@ namespace BizHawk.Client.Common
 
 		public override string Diff => $"{_value - _previous:+#;-#;0}";
 
-		public override bool IsValid => Domain.Size == 0 || Address < Domain.Size;
-
-		public override uint MaxValue => byte.MaxValue;
-
 		public override int Value => GetByte();
 
 		public override string ValueString => FormatValue(GetByte());

src/BizHawk.Client.Common/tools/Watch/DWordWatch.cs

@@ -100,10 +100,6 @@ namespace BizHawk.Client.Common
 
 		public override string Diff => $"{_value - (long)_previous:+#;-#;0}";
 
-		public override bool IsValid => Domain.Size == 0 || Address < (Domain.Size - 3);
-
-		public override uint MaxValue => uint.MaxValue;
-
 		public override int Value => (int)GetDWord();
 
 		public override string ValueString => FormatValue(GetDWord());

src/BizHawk.Client.Common/tools/Watch/SeparatorWatch.cs

@@ -90,11 +90,6 @@ namespace BizHawk.Client.Common
 		/// </summary>
 		public override string Diff => "";
 
-		/// <summary>
-		/// Ignore that stuff
-		/// </summary>
-		public override uint MaxValue => 0;
-
 		/// <summary>
 		/// Ignore that stuff
 		/// </summary>

src/BizHawk.Client.Common/tools/Watch/Watch.cs

@@ -502,7 +502,15 @@ namespace BizHawk.Client.Common
 		/// <summary>
 		/// Gets the maximum possible value
 		/// </summary>
-		public abstract uint MaxValue { get; }
+		public uint MaxValue
+			=> Size switch
+			{
+				WatchSize.Separator => 0,
+				WatchSize.Byte => byte.MaxValue,
+				WatchSize.Word => ushort.MaxValue,
+				WatchSize.DWord => uint.MaxValue,
+				_ => throw new InvalidOperationException()
+			};
 
 		/// <summary>
 		/// Gets the current value
@@ -517,7 +525,8 @@ namespace BizHawk.Client.Common
 		/// <summary>
 		/// Returns true if the Watch is valid, false otherwise
 		/// </summary>
-		public abstract bool IsValid { get; }
+		public virtual bool IsValid
+			=> Domain.Size is 0 || Address <= Domain.Size - unchecked((long) Size);
 
 		/// <summary>
 		/// Try to sets the value into the <see cref="MemoryDomain"/>

src/BizHawk.Client.Common/tools/Watch/WordWatch.cs

@@ -98,10 +98,6 @@ namespace BizHawk.Client.Common
 
 		public override string Diff => $"{_value - _previous:+#;-#;0}";
 
-		public override bool IsValid => Domain.Size == 0 || Address < (Domain.Size - 1);
-
-		public override uint MaxValue => ushort.MaxValue;
-
 		public override int Value => GetWord();
 
 		public override string ValueString => FormatValue(GetWord());