Benchmark framework + First memory fixes

[hannahhoward]

Goals

Establish a framework for benchmarking graphsync, and also first round fixes for memory performance

Implementation

• Establish a test network that can be controlled in terms of latency/bandwidth/connectivity conditions
• Establish a generator for multiple graphsync instances to run large scale benchmarks under different conditions
• Write a single initial benchmark to measure performance -- note this doesn't exercise the whole range of conditions available in the testbed -- but just to demonstrate it's use
• We can see the first fixes in terms of performance emerge just by profile the memory performance of this benchmark
  • We combine a couple changes here along with some updates to go-ipld-prime and go-ipld-prime-proto to avoid hundreds of unneccesary mem-copies and allocations of byte arrays.