Add layer_norm operator

[voltjia]

pytest output:

============================= test session starts ==============================
platform linux -- Python 3.10.12, pytest-8.3.3, pluggy-1.5.0
rootdir: /home/huangjiacheng/ntops
configfile: pyproject.toml
plugins: cov-6.0.0
collected 590 items

tests/test_abs.py ........                                               [  1%]
tests/test_add.py ........                                               [  2%]
tests/test_addmm.py ..                                                   [  3%]
tests/test_bitwise_and.py ................                               [  5%]
tests/test_bitwise_not.py ................                               [  8%]
tests/test_bitwise_or.py ................                                [ 11%]
tests/test_bmm.py ..                                                     [ 11%]
tests/test_clamp.py ........                                             [ 12%]
tests/test_cos.py ........                                               [ 14%]
tests/test_div.py ........                                               [ 15%]
tests/test_dropout.py ........                                           [ 16%]
tests/test_eq.py ........                                                [ 18%]
tests/test_exp.py ........                                               [ 19%]
tests/test_ge.py ........                                                [ 21%]
tests/test_gelu.py ........                                              [ 22%]
tests/test_gt.py ........                                                [ 23%]
tests/test_isinf.py ........                                             [ 25%]
tests/test_isnan.py ........                                             [ 26%]
tests/test_layer_norm.py ............................................... [ 34%]
.................................................                        [ 42%]
tests/test_le.py ........                                                [ 44%]
tests/test_lt.py ........                                                [ 45%]
tests/test_mm.py ..                                                      [ 45%]
tests/test_mul.py ........                                               [ 47%]
tests/test_ne.py ........                                                [ 48%]
tests/test_neg.py ........                                               [ 49%]
tests/test_pow.py ........                                               [ 51%]
tests/test_relu.py ........                                              [ 52%]
tests/test_rms_norm.py ................................................. [ 60%]
...............                                                          [ 63%]
tests/test_rotary_position_embedding.py ................................ [ 68%]
........................................................................ [ 81%]
........................                                                 [ 85%]
tests/test_rsqrt.py ........                                             [ 86%]
tests/test_scaled_dot_product_attention.py ............................. [ 91%]
...                                                                      [ 91%]
tests/test_sigmoid.py ........                                           [ 93%]
tests/test_silu.py ........                                              [ 94%]
tests/test_sin.py ........                                               [ 95%]
tests/test_softmax.py ........                                           [ 97%]
tests/test_sub.py ........                                               [ 98%]
tests/test_tanh.py ........                                              [100%]

======================= 590 passed in 430.73s (0:07:10) ========================