backtracking register allocator

 regalloc2 is a register allocator
 that started life as, and is about 50% still,
 a port of IonMonkey's backtracking register allocator to Rust.
 In many regards, it has been generalized, optimized, and improved
 since the initial port.
 .
 In addition,
 it contains substantial amounts of testing infrastructure
 (fuzzing harnesses and checkers)
 that does not exist in the original IonMonkey allocator.
 .
 This package contains the command-line tool regalloc2-tool
 which reads a bincode-encoded SerializableFunction
 and then runs the register allocator and checker on it.
 .
 This is a useful tool for debugging register allocation failures
 and to investigate cases of poor register allocation.