hex-opbatch

This release introduces significant enhancements to the Hexagon backend, including multi-NPU device support, a fully asynchronous backend, and improved performance for various operations like ALLREDUCE and matrix multiplications. It also includes numerous bug fixes and optimizations across different Hexagon modules.

This release significantly improves hexagon performance through op request batching, buffer management rewrite, and explicit L2 cache control. It also removes the deprecated GGML_HEXAGON_EXPERIMENTAL environment variable.