`impl {Div,Mul,DivAssign,MulAssign}<{u16, u8}> for Duration` should also exist

[nagisa]

Currently only impl {Div,Mul,DivAssign,MulAssign}<u32> for Duration exist, and there is no functional reason why the other implementations should not exist.

[sfackler]

At least as of a couple years ago, this breaks type inference for duration / 2: #32515