Set turtle graphics inside runCode to avoid null.firstChild

[cocomarine]

Closes Intermittent ExternalError when running Turtle projects after saving #1261

Findings

• The 'firstChild' error is not at all reproducible locally
• In staging, sometimes it errors and sometimes not. Couldn't see any pattern 🤷‍♀️
• Upon inspecting turtle.js within the skupt module, it seemed that the type error could be coming from the target being null while checking target.firstChild for the while loop:

// turtle.js 
...
function getConfiguredTarget() {
    var selector, target;

    selector = (Sk.TurtleGraphics && Sk.TurtleGraphics.target) || "turtle",
    target   = typeof selector === "string" ?
        document.getElementById(selector) :
        selector;
    // ensure that the canvas container is empty
    while (target.firstChild) {
        target.removeChild(target.firstChild);
    }
    return target;
}
...

• SkulptRunner runs runCode() in a parent useEffect. VisualOutputPane sets Sk.TurtleGraphics.target in a child useEffect. React runs parent effects before child effects, so from turtle import * can run before the child has set Sk.TurtleGraphics.target.

Potential fix

• Ensured Sk.TurtleGraphics.target points at #turtleOutput before turtle runs by setting it within the SkulpRunner's runCode()

[Copilot]

Pull request overview

This PR addresses an intermittent Skulpt Turtle graphics failure (reported as null.firstChild) by ensuring the Turtle graphics target/asset wiring happens before Skulpt imports/executes user code, particularly in the web component (shadow DOM) context.

Changes:

• Initialize Sk.TurtleGraphics.target and Sk.TurtleGraphics.assets inside runCode() before invoking Sk.misceval.asyncToPromise / importing the main module.
• Add a regression test asserting Turtle wiring occurs before asyncToPromise is entered.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/components/Editor/Runners/PythonRunner/SkulptRunner/SkulptRunner.jsx	Wires Turtle graphics target/assets earlier (and supports shadowRoot lookup) to prevent null access during turtle import/runtime init.
src/components/Editor/Runners/PythonRunner/SkulptRunner/SkulptRunner.test.js	Adds a unit test ensuring Turtle configuration is set before Skulpt execution begins.

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[DNR500]

Nice! I can see how this should avoid a race condition between turtle setup and code execution in VisualOutputPane. Also, thanks for adding the comments and tests