Allow args into grad_f for ULD

[lockwo]

In the ULD drift term you provide the grad f, which is then called https://github.com/patrick-kidger/diffrax/blob/main/diffrax/_term.py#L966. It would be nice to be able to have that function also accept args as well beyond the differentiated input (e.g. grad_f(x, args) where args is just auxiliary information like is used in other areas). I can also curry the args in for my case, but it seems like in general most things allow args as input in diffrax, so I wanted to inquire about making this consistent.

[patrick-kidger]

@andyElking WDYT? I have vague memories of us discussing this but I may be misremembering.