fix: attach save() to p5.Graphics.prototype #8881

[BHARATH0153]

Resolves #8881

Changes

Fixed save() not working on p5.Graphics

Previously save() was only attached to p5.prototype via the files module (registered through p5.registerAddon), so pg.save("test.png") threw TypeError: pg.save is not a function.

Now the files module is also called with p5.Graphics.prototype inside the graphics() registration function, following the exact same pattern as all other modules (primitives2D, attributes, image, pixels, etc.).

PR Checklist

• npm run lint passes
• Inline reference is included / updated
• Unit tests are included / updated

[BHARATH0153]

@perminder-17 please review