refactor: replace deepCopyFunction with structuredClone

[willeastcott]

Summary

• Replace custom deepCopyFunction in util.ts with the built-in structuredClone
• Delete src/util.ts (it only contained deepCopyFunction)

structuredClone is supported in all modern browsers and Node 17+.

Test plan

• Verify npm run build completes successfully
• Verify context menus on nodes and edges still function correctly (the two call sites that used deepCopyFunction)

[Copilot]

Pull request overview

This PR refactors context-menu item cloning by replacing the custom deepCopyFunction utility with the platform structuredClone, and removes the now-unused utility file.

Changes:

• Replaced deepCopyFunction(...) with structuredClone(...) for edge/node context menu item cloning.
• Removed src/util.ts and the corresponding README entry.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/util.ts	Removes the custom deep copy helper that was previously used for menu item cloning.
src/index.ts	Switches edge/node context menu item cloning to structuredClone and removes the old import.
README.md	Removes util.ts from the source layout list.

Comments suppressed due to low confidence (2)

src/index.ts:323

• Using structuredClone here can throw at runtime when edgeSchema.contextMenuItems contains non-cloneable values (notably callback functions like onSelect, which PCUI Menu items commonly use). The previous deepCopyFunction preserved function references, so this is a breaking behavior change. Consider switching to a cloning approach that preserves functions (e.g., shallow-clone items/arrays) or explicitly constrain/validate contextMenuItems to structured-cloneable data before cloning (and document the restriction).

            const contextMenuItems = structuredClone(edgeSchema.contextMenuItems).map((item: any) => {
                if (item.action === GRAPH_ACTIONS.DELETE_EDGE) {
                    item.onSelect = () => {
                        this._dispatchEvent(GRAPH_ACTIONS.DELETE_EDGE, { edgeId: edgeId, edge: this._graphData.get(`data.edges.${edgeId}`) });
                    };

src/index.ts:433

• _initializeNodeContextMenuItems adds onSelect functions to each item, and it’s invoked both from Graph.createNode and again inside GraphViewNode.addContextMenu. With structuredClone, the second invocation will attempt to clone items that now include functions and will throw a DataCloneError, breaking node context menus. Fix by ensuring menu items are only initialized/cloned once (single call site), or by replacing structuredClone with a clone that tolerates function properties for these menu item objects.

        const contextMenuItems = structuredClone(items).map((item: any) => {
            if (item.action === GRAPH_ACTIONS.ADD_EDGE) {
                item.onSelect = () => this._createUnconnectedEdgeForNode(node, item.edgeType);
            }
            if (item.action === GRAPH_ACTIONS.DELETE_NODE) {
                item.onSelect = () => {
                    this._dispatchEvent(GRAPH_ACTIONS.DELETE_NODE, this._deleteNode(node.id));
                };
            }

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