Add sub 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 262 items

tests/test_abs.py ........                                               [  3%]
tests/test_add.py ........                                               [  6%]
tests/test_addmm.py ..                                                   [  6%]
tests/test_bitwise_and.py ................                               [ 12%]
tests/test_bitwise_not.py ................                               [ 19%]
tests/test_bitwise_or.py ................                                [ 25%]
tests/test_bmm.py ..                                                     [ 25%]
tests/test_clamp.py ........                                             [ 29%]
tests/test_cos.py ........                                               [ 32%]
tests/test_div.py ........                                               [ 35%]
tests/test_dropout.py ........                                           [ 38%]
tests/test_eq.py ........                                                [ 41%]
tests/test_exp.py ........                                               [ 44%]
tests/test_ge.py ........                                                [ 47%]
tests/test_gelu.py ........                                              [ 50%]
tests/test_gt.py ........                                                [ 53%]
tests/test_isinf.py ........                                             [ 56%]
tests/test_isnan.py ........                                             [ 59%]
tests/test_le.py ........                                                [ 62%]
tests/test_lt.py ........                                                [ 65%]
tests/test_mm.py ..                                                      [ 66%]
tests/test_mul.py ........                                               [ 69%]
tests/test_ne.py ........                                                [ 72%]
tests/test_neg.py ........                                               [ 75%]
tests/test_pow.py ........                                               [ 78%]
tests/test_relu.py ........                                              [ 81%]
tests/test_rsqrt.py ........                                             [ 84%]
tests/test_sigmoid.py ........                                           [ 87%]
tests/test_sin.py ........                                               [ 90%]
tests/test_softmax.py ........                                           [ 93%]
tests/test_sub.py ........                                               [ 96%]
tests/test_tanh.py ........                                              [100%]

======================= 262 passed in 285.13s (0:04:45) ========================