Improve MemorySegment::toString

A segment could either be a heap segment or a native segment. Never both at the same time. However, a heap segment might have an offset if it was sliced. So, instead of this:

heapSegment = MemorySegment{ heapBase: Optional[[B@7ea987ac] address: 0x2, byteSize: 2 }
nativeSegment = MemorySegment{ heapBase: Optional.empty address: 0x6000006a1da0, byteSize: 2 }

It would be better to do this:

heapSegment = MemorySegment{ heapBase: [B@7ea987ac, address: 0x2, byteSize: 2 }
nativeSegment = MemorySegment{ address:0x6000006a1da0, byteSize: 2 }