Define `CheckedAdd` and `CheckedSub` traits

There are a few places where I've seen, or they could benefit from a, checked_add and checked_sub implementations throughout the library, such as on VirtAddr, PhysFrame, PhysAddr... etc. I would like to define a CheckedAdd and CheckedSub trait similar to the std::ops::Add trait that defines a checked_* method.

pub trait CheckedAdd<Rhs = Self> {
    type Output;

    fn checked_add(self, rhs: Rhs) -> Option<Self::Output>;
}

pub trait CheckedSub<Rhs = Self> {
    type Output;

    fn checked_sub(self, rhs: Rhs) -> Option<Self::Output>;
}

I would like to add this specifically to provide for checked_operations across multiple Rhs types. An example being a CheckedAdd<Rhs=PhysFrame> for PhysFrame and CheckedAdd<Rhs=PhysAddr> for PhysFrame.

Start by locating the relevant checked_add and checked_sub implementations or call sites for VirtAddr, PhysFrame, and PhysAddr, then compare the proposed traits with std::ops::Add. Done means the trait design supports the stated cross-type PhysFrame and PhysAddr operations and the affected library behavior is covered by verification.