fix(checkpoint): preserve keyword arguments with DeepSpeed

[iMountTai]

The DeepSpeed checkpoint path flattens args and kwargs.values(), then invokes the model with all values as positional arguments. This loses keyword names: a call such as forward(x, *, scale, offset) fails, and keyword arguments passed in a different order can bind to the wrong parameters.

Capture the positional-argument count and ordered keyword names in the checkpoint closure. Reconstruct the original positional and keyword arguments for both the initial forward and backward recomputation. The existing no-gradient bypass is retained.