* [fx] fix wrong variable name in solver rotor
* [fx] fix wrong variable name in solver rotor
* [fx] fix the discretize bug
* [fx] fix the first op in activation checkpoint codegen
* [fx] fix some bugs of ckpt solver
* [fx] modify test_ckpt_torchvision
* [fx] set sequence to __sequence__ attr of GraphModule
* [fx] docstring modification
* [fx] remove performance test