Fix/webgpu crash pixel density

[saurabh24thakur]

Fixes #8456

Description

Fixes a crash when using the WebGPU renderer where calling pixelDensity() immediately after setAttributes() (or any other function that triggers an asynchronous context reset) would result in TypeError: Cannot read properties of undefined (reading 'createTexture').

The Issue

In p5.js 2.0, setAttributes() triggers an asynchronous reset of the rendering context via _resetContext(). Because core functions like pixelDensity() are synchronous, they can trigger a resize() (and subsequently _updateSize()) on a new renderer instance before its WebGPU device has been successfully initialized.

Changes

1. RendererWebGPU: Added guard clauses to _updateSize(), clear(), and clearDepth() to return early if this.device is not yet defined. Since _initContext() calls these methods upon successful initialization, the state is eventually synchronized correctly once the device is ready.
2. Renderer3D:
   • Updated _resetContext() to await the new renderer's contextReady promise before replacing the existing renderer on the p5 instance. This ensures that the sketch's _renderer property always points to a valid, initialized renderer.
   • Ensured the new renderer inherits the pixelDensity of the renderer it is replacing to avoid size-mismatch warnings in the console (e.g., depth-stencil attachment size mismatches).
3. Tests: Added a new unit test in test/unit/webgpu/issue_repro.js that specifically reproduces this race condition.

Checklist

• I have read the CONTRIBUTING document.
• My code follows the style guidelines of this project.
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works.
• New and existing unit tests pass locally with my changes.