feat: support fused gelu tanh mul

[zhyncs]

cc @yzh119

pytest python/tests/test_activation.py
=================================================================== test session starts ===================================================================
platform linux -- Python 3.10.12, pytest-8.3.2, pluggy-1.5.0
rootdir: /flashinfer/python
plugins: anyio-4.2.0
collected 630 items

python/tests/test_activation.py ................................................................................................................... [ 18%]
................................................................................................................................................... [ 41%]
................................................................................................................................................... [ 64%]
................................................................................................................................................... [ 88%]
..........................................................................                                                                          [100%]

============================================================= 630 passed in 146.89s (0:02:26) =============================================================

[zhyncs]

@yzh119 Thank you for your changes!