Use libyaml when available for faster schema parsing

This uses the LibYAML-based parser when it is available instead of the default Python parser, as suggested in the pyyaml docs. I found this trick randomly in my RSS feeds from this post, and this appears to make loading the Arkindex API schema twice as fast, from 2.5-3 seconds to 1.2-1.5 seconds. LibYAML is already available in python:3.10 and python:3.10-alpine, so it's safe to say that this could speed up most of our Docker images without further intervention.