Add a standalone binary to compute LLMV observations

[ChrisCummins]

This adds a new standalone compute_observation binary that takes an observation space name and a LLVM bitcode and computes an observation. There is a corresponding compiler_gym.envs.llvm.compute_observation() python function to run the binary.

It is intended for use cases where you want to compute an observation without the overhead of initializing a full environment.

Example usage:

>>> env = compiler_gym.make("llvm-v0")
>>> space = env.observation.spaces["Ir"]
>>> bitcode = Path("bitcode.bc")
>>> observation = llvm.compute_observation(space, bitcode, timeout=30)