MemoryRegion::is_disjoint_from can overflow on u64 addition

[Sword-Smith]

The following test panics, because of the value of the free_mem_page_ptr field.

    #[test]
    fn problem {
        let mem_layout = DynamicTasmConstraintEvaluationMemoryLayout {
            free_mem_page_ptr: BFieldElement::new(BFieldElement::MAX),
            challenges_ptr: BFieldElement::new(1 << 63),
        };
        mem_layout.is_integral();
    }

The problem arises because the free_mem_page_ptr region is assumed to have a size of MEM_PAGE_SIZE = $2^{32}$. And $-1 + 2^{32} = 2^{64} - 2^{32} + 2^{32} = 0\ mod\ 2^{64}$, which is an overflow.

The overflowing addition happens here.