The CentML compilation backend I am working on wants to wrap the
CompiledGraphs forward function (the one returned by get_wrapper) in a
torch.fx.GraphModule. This GraphModule would then be pickled and sent
from a server to a client.

However, it isn't possible to pickle the lambda/local function returned
by get_wrapper. Therefore, I am turning get_wrapper into a class
CompiledForwardFunction whose forward function behaves like the wrapper
returned by get_wrapper.

Additionally, in order to pickle CompiledForwardFunction, I have defined
pickling and unpickling behaviour for CompiledGraph using __getstate__
and __setstate__ respectively. These just call CompiledGraph's existing
save and load functions.