[example] add jagged_softmax example

[pianpwk]

very new to this, but thought it was worth putting up, at least for feedback :)

results from running HELION_USE_DEFAULT_CONFIG=0 python benchmarks/run.py --kernel jagged_softmax --num-inputs 10 --metrics speedup:

  x_val    torch_jagged_softmax_torch_sum-speedup    triton_jagged_softmax_simple_fused-speedup    triton_jagged_softmax_variable_length_loop-speedup    torch_compile_nested_tensor_integration-speedup    helion_jagged_softmax_tritonbench-speedup
-------  ----------------------------------------  --------------------------------------------  ----------------------------------------------------  -------------------------------------------------  -------------------------------------------
      4                                   1.84622                                      0.974523                                              0.954934                                           0.322953                                      1.96138
      4                                   2.95117                                      1.45007                                               1.43405                                            0.495255                                      3.30609
      4                                   1.6221                                       0.813262                                              0.871952                                           0.307515                                      2.00381
      4                                   1.66235                                      0.848234                                              0.872248                                           0.314032                                      1.97156
      4                                   1.59061                                      0.856801                                              0.914473                                           0.293083                                      1.90051
      4                                   1.68989                                      0.848728                                              0.877103                                           0.302414                                      1.35153
      4                                   1.69289                                      0.831421                                              0.866428                                           0.308762                                      1.38123
      4                                   1.59673                                      0.861041                                              0.862671                                           0.301662                                      1.40576
      4                                   1.66998                                      0.872588                                              0.899465                                           0.293748                                      1.57284
      4                                   1.6537                                       0.866808                                              0.877925                                           0.306829                                      1.88681
average                                   1.79756                                      0.922347                                              0.943125                                           0.324625                                      1.87415

[jansel]

lint/test failures?

[pianpwk]

wasn't sure how to write this without the store, and it seems this store breaks ref eager mode testing