arc-b580-v0.6

What's new in v0.6

• Long-context decode is faster on the B580: plain decode +12% at 48K and +21% at 115K. MTP is +2–4%. Output and accuracy are unchanged.
• Fix: crash at the first decode on GPUs whose driver lacks the intel_sub_group_i8_i4_matrix_mad_k32 builtin (reported on Lunar Lake / Arc 140V). The kernels now use inline vISA instead.
• Guide: when to turn thinking on (reasoning puzzles).

Windows x64 build of the arc-b580 branch for Intel Arc (SYCL). EXPERIMENTAL: built by CI and not yet tested on a
Windows machine. Needs a current Intel Arc driver (an old driver's ze_loader.dll crashes at start).
Unzip, put the model next to it, and run run-bonsai.bat. See README.txt and
docs/bonsai-arc-b580.md. Please report results in https://github.com/Torchit1/llama.cpp/discussions/1