Implement native DAT container codec

engine/Age.Engine.Tests/OpcodeTableTests.cs

@@ -4,15 +4,16 @@ using Xunit;
 public class OpcodeTableTests
 {
     [Fact]
-    public void LoadsAll248FromJson()
+    public void LoadsObservedOpcodesPlusMappedUnusedAbiEntries()
     {
         var t = OpcodeTableJson.Load(Paths.OpcodesJson);
-        Assert.Equal(248, t.Count);
+        Assert.Equal(249, t.Count); // 248 corpus-observed + unused persistence ABI opcode 0x19f
         Assert.True(t.TryGet(0x55, out var label, out var argc));
         Assert.Equal("mov", label);
         Assert.Equal(2, argc);
         Assert.Equal("u0041BEB0", t.Label(0x90));
         Assert.Equal(7, t.Argc(0x90));
+        Assert.Equal(2, t.Argc(0x19f));
         Assert.Equal(-1, t.Argc(0x9999)); // absent -> -1
     }
 }