use criterion and/or iai for benchmarks

[cosmicexplorer]

Problem

See #93 (comment). criterion and iai are alternative benchmarking harnesses.

Solution

• criterion has nicer output than the default harness, and some statistical metrics which can be tuned to the precise benchmark requirements.
• iai is a radically different approach using cachegrind which counts instructions instead of timings.

Result

These benchmark harnesses may complement the performance improvements from #93, and may make it easier to investigate further performance wins in the future.