BaseHeap::AllocRange was rounding the inclusive high_address UP via
xe::align(), which could push the search range one alignment stride
past the requested end. The new free-block-tracker top-down search
treats high_page_number as an inclusive max (usable_end =
high_page_number + 1), so the round-up caused it to return a base
page one stride beyond the caller's bound — most visibly when
PhysicalHeap::Alloc passed parent_heap_end = GetPhysicalAddress(...)
just below a page boundary, producing a translated address one page
past the child heap and tripping "passed out of range address range"
in BaseHeap::AllocFixed.
Drop the xe::align on the high side so high_address stays a true
inclusive bound. The low_address round-up is still correct since
allocations must START at or above the aligned low.
