Every test created its own wgpu instance and device (with adapter-maximum
limits) concurrently, which could wedge the driver and hang the suite
indefinitely. Tests now hold a process-wide lock while they own a device, and
GpuAccelerator readback waits are bounded at 30s so a stuck driver surfaces as
GpuError::BufferMap instead of blocking forever.
Co-Authored-By: Claude Fable 5.1 <[email protected]>
