have_gpu

True when this pperl can actually reach a graphics card: the build has the GPU option AND an adapter was found.

It answers rather than dying, so a program can choose a CPU fallback:

my $sum = Peta::WebGPU::have_gpu() ? gpu_sum(@data) : cpu_sum(@data);

A machine with no GPU driver at all, or a headless container, will say false here even on a build that has the option compiled in.