Function select_shard 

pub fn select_shard(last_byte: u8, num_shards: u32) -> u32

Computes the shard ID from the last byte of an address.

Uses optimized bit masking for the common case of 3 shards (instead of modulo).

Arguments

• last_byte - The last byte of the address
• num_shards - The total number of shards in the network

Returns

The shard ID (0 to num_shards-1)