The loader thread now only loads the game. PSP_InitUpdate creates the GPU on
the thread that owns the graphics device, so device loss can't race the
creation, and the device-lost flag and the GPU init on libretro's separate
path are gone. Vulkan loads its shader cache without waiting for the
pipelines, and PSP_InitUpdate keeps the boot in Booting until they're
created. Exiting during boot joins the loader thread in PSP_Shutdown.
Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>