Add sampled_op benchmark

[rusty1s]

Function: add
=========================
Vanilla forward:  0.3757s
Vanilla backward: 0.4279s
=========================
pyg_lib forward:  0.1756s
pyg_lib backward: 0.3006s

Function: sub
=========================
Vanilla forward:  0.3762s
Vanilla backward: 0.4979s
=========================
pyg_lib forward:  0.1764s
pyg_lib backward: 0.3141s

Function: mul
=========================
Vanilla forward:  0.3755s
Vanilla backward: 0.7078s
=========================
pyg_lib forward:  0.1775s
pyg_lib backward: 0.6206s

Function: div
=========================
Vanilla forward:  0.3758s
Vanilla backward: 1.1376s
=========================
pyg_lib forward:  0.1868s
pyg_lib backward: 1.0707s