Test for stale observations due to observation_handshake

[rallen10]

I am concerned that the current logic for ksp_interface_loop.observation_handshake used between ksp_interface_loop and AgentEnvRunner.policy_loop may cause old/stale observations to be processed by AgentEnvRunner.policy_loop.

In particular, see how AgentEnvRunner.policy_loop receives messages from the observation_handshake (in v0.11.1): https://github.com/mit-ll/spacegym-kspdg/blob/v0.11.1/src/kspdg/agent_api/runner.py#L125

If there are multiple messages in this pipe, wouldn't this if statement get the oldest one? Shouldn't it use something like a while statement to make sure it's clearing the pipe and processing the newest observation?