* SYCL: fix a bug with async memcpy
* make mmid_row_mapping_host persistent
* comment on stream->wait
* Apply suggestion from @sanmai
* Apply suggestion from @sanmai
* Apply suggestion from @sanmai
* [SYCL] Centralize Level Zero detection in ggml_sycl_init
* use the same wording
* get back the warning
* [SYCL] Remove per-allocation getenv() for GGML_SYCL_ENABLE_LEVEL_ZERO
* bring back the comment
* move it up to make sure devices call the shots
* move the env detection early
* replace g_ggml_sycl_enable_level_zero with a direct call to .ext_oneapi_level_zero
* update the comment
* switch back to g_ggml_sycl_enable_level_zero with a sentinel
* remove the check
* Reduce the diff
* reword, move lower
* move things aroudn
* remove forward declaration if favor of a full replace
* pre-cache results of zeDeviceGetProperties
* put ggml_sycl_get_env back
* replace get_sycl_env with ggml_sycl_get_env
* add whitespace back
* Apply suggestion from @sanmai
- change `k_copy_src1_to_contiguous` so that uses a precomputed contiguous mapping where all rows "owned" by an expert are in one slice with a know starts and ends
- switch the `O(n_as * n_routed_rows)` contraption to a counting sort-based procedure with `O(n_as + n_routed_rows)` complexity
* SYCL: reduce allocation overhead during flash attention
* tidy up whitespace
* add a note about the flag
* move ggml_sycl_fattn_* into fattn-buffers.hpp
* refactor implementation into fattn-buffers.cpp
* move new_fattn_kv_buffers back into ggml-sycl.cpp
