Constant DEP_NODE_WIDTH_BITS

const DEP_NODE_WIDTH_BITS: usize = _; // 2usize

Number of bits we need to store the number of used bytes in a SerializedDepNodeIndex. Note that wherever we encode byte widths like this we actually store the number of bytes used minus 1; for a 4-byte value we technically would have 5 widths to store, but using one byte to store zeroes (which are relatively rare) is a decent tradeoff to save a bit in our bitfields.