feat: add unsafe fn remove_from_ptr for linked list

[MrCroxx]

Add a useful helper.

    /// Remove an element from the pointer to it.
    ///
    /// # Safety
    ///
    /// `ptr` must be a pointer to an object that is part of this list.
    #[inline]
    pub unsafe fn remove_from_ptr(
        &mut self,
        ptr: *const <A::PointerOps as PointerOps>::Value,
    ) -> <A::PointerOps as PointerOps>::Pointer {
        self.cursor_mut_from_ptr(ptr).remove().unwrap()
    }

Signed-off-by: MrCroxx [email protected]