[SYCL free func] migrate NMS kernels

[jiafuzha]

SYCL free functions: Both kernels ( nms_sub_kernel  and  gather_keep_from_mask_kernel ) are already converted to free functions using  SYCL_EXT_ONEAPI_FUNCTION_PROPERTY  — no class functors remain.

 Unit Tests                                                                                                                                             
                                                                                                                                                        
 Ran  test/regressions/test_nms.py  from both repos — all passed:                                                                                       
                                                                                                                                                        
  test/regressions/test_nms.py::TestNNMethod::test_batched_nms  PASSED                                                                                  
  test/regressions/test_nms.py::TestNNMethod::test_nms          PASSED                                                                                  
  2 passed in ~3s