GeezerVison

Adds AF_WITH_GRAPHICS (default ON) so ArrayFire can be built as a pure compute library. Users embedding it have been patching out the graphics stack by hand because Forge headers, glad and OpenGL were fetched and compiled unconditionally (this came up again from Pix4D, and #2878 has been open for years).

With the option OFF the build skips OpenGL, glad and the Forge dependency, drops the graphics sources from every backend, and compiles stubs for the thirty public graphics functions that return AF_ERR_NOT_CONFIGURED, the same way image IO behaves without FreeImage; the exported symbol set is unchanged, so the unified backend and existing binaries keep working. AF_BUILD_FORGE becomes dependent on it and the graphics examples are skipped.

Verified on Windows: CPU, OpenCL and CUDA 13 backends build with the option OFF and ON, the unified library and the CPU examples build with it OFF, a check program gets 302 from af_create_window and af_show through both afcpu and the unified af while the rest of the API works, and the sparse/backend/info suites pass. The full oneAPI library builds with the option OFF and ON (icx 2026.0). A no-graphics leg is added to the Linux CPU CI matrix.