Unstable NodeWithValue.toString()

YANGTOOLS-1562 highlights we are treating byte[] values differently in NodeWithValue from how we handle it Leaf(SetEntry)Node.

The real problem is NodeWithValue, which boils down to byte[].toString(), which can fluctuate. ImmutableLeafNode.toString() uses ToStringHelper, which falls back to Arrays.toString(), producing a stable value.

Both formats are not great – for 13.0.1 use b64:<ENCODED> values. For backports use Arrays.toString().