Fix class cast exception with ObjectSource

We were generating methods with the original object, rather than the
extra one.

Updated our tests to actually catch this. Unfortunately the only places
we use this interface is in HTTP responses and transferred files,
neither of which show up in the Lua-side tests.

projects/core/src/main/java/dan200/computercraft/core/asm/MethodSupplierImpl.java

@@ -76,7 +76,7 @@ public boolean forEachMethod(Object object, TargetedConsumer<T> consumer) {
             for (var extra : source.getExtra()) {
                 var extraMethods = getMethods(extra.getClass());
                 if (!extraMethods.isEmpty()) hasMethods = true;
-                for (var method : extraMethods) consumer.accept(object, method.name(), method.method(), method);
+                for (var method : extraMethods) consumer.accept(extra, method.name(), method.method(), method);
             }
         }
 

projects/core/src/test/java/dan200/computercraft/core/asm/MethodTest.java

@@ -58,7 +58,7 @@ public void testDynamicPeripheral() {
 
     @Test
     public void testExtra() {
-        ComputerBootstrap.run("assert(extra.go, 'go')\nassert(extra.go2, 'go2')",
+        ComputerBootstrap.run("assert(extra.go() == nil, 'go')\nassert(extra.go2() == 456, 'go2')",
             x -> x.addApi(new ExtraObject()),
             50);
     }
@@ -163,7 +163,8 @@ public String[] getNames() {
         }
 
         @LuaFunction
-        public final void go2() {
+        public final int go2() {
+            return 456;
         }
 
         @Override