Python 3.10 benchmarking

[movermeyer]

I needed to update the benchmarking scripts for Python 3.10:

• pip wasn't being found in the Dockerfile
• The scripts were assuming that minor versions would only have a single character:
  • It was sorting the minor versions as strings
  • It was using a regex that was assuming a single character
• iso8601utils doesn't support Python 3.10: https://github.com/silverfernsys/iso8601utils/issues/6