Track Hyperlight microbenchmarks #706

We should track the performance of Hyperlight on microbenchmarks in a somewhat-reliable environment, so that we understand where the time is actually going and where we can improve it.

Things that we should track include at least:

• RTT for a guest call, with various sizes of parameters
• Time to map/unmap various kinds of host memory regions
• Time to create, snapshot, restore, and drop a sandbox
• All of the above in a multithreaded use case, with various degrees of parallelism (including both under- and over-subscribed compared to the number of cores)