ES6 class convertion of LGraph (#63)

* LGraph ES6 class conversion

* Add compatibility to prototype extension

* Add jest test action

---------

Co-authored-by: filtered <176114999+webfiltered@users.noreply.github.com>

test/LGraph.test.ts

@@ -0,0 +1,39 @@
+import {
+  LGraphES6 as LGraph,
+  LGraph as LegacyLGraph,
+  LiteGraph,
+} from "../dist/litegraph.es.js";
+
+describe("LegacyLGraph Compatibility Layer", () => {
+  test("LegacyLGraph can be instantiated", () => {
+    const graph = new LegacyLGraph({extra: "TestGraph"});
+    expect(graph).toBeInstanceOf(LGraph);
+    expect(graph).toBeInstanceOf(LegacyLGraph);
+    expect(graph.extra).toBe("TestGraph");
+  });
+
+  test("LegacyLGraph can be extended via prototype", () => {
+    LegacyLGraph.prototype.newMethod = function () {
+      return "New method added via prototype";
+    };
+
+    const graph = new LegacyLGraph();
+    expect(graph.newMethod()).toBe("New method added via prototype");
+  });
+
+  test("Extensions to LegacyLGraph affect LGraph instances", () => {
+    LegacyLGraph.prototype.anotherMethod = function () {
+      return "Another method";
+    };
+
+    const legacyGraph = new LegacyLGraph();
+    const normalGraph = new LGraph();
+
+    expect(legacyGraph.anotherMethod()).toBe("Another method");
+    expect(normalGraph.anotherMethod()).toBe("Another method");
+  });
+
+  test("LegacyLGraph is correctly assigned to LiteGraph", () => {
+    expect(LiteGraph.LGraph).toBe(LegacyLGraph);
+  });
+});