Bijou64: A variable-length integer encoding

Bijou64 is a new variable-length integer encoding developed for the Subduction sync protocol that ensures each number has only one possible representation, addressing a security vulnerability in common formats like LEB128 that allow multiple encodings for the same value. This canonical design constraint, intended to prevent signature verification exploits, unexpectedly also makes bijou64 several times faster than LEB128 by reducing computational overhead. The encoding demonstrates how security-focused design decisions can inadvertently yield performance benefits while eliminating the need for separate canonicality validation checks that are often missed or removed in implementations.