Build Performance and Scale Testing

We need a system for perf testing css blocks build time performance at scale with predictable and yet configurable parameters so that we can give meaningful numbers to people who are considering adopting CSS Blocks.

Start by reviewing the CSS Blocks build process and how CSS blocks are currently compiled. Define predictable, configurable scale-testing parameters and identify how build-time results should be recorded. Done means the system produces meaningful, repeatable performance numbers for CSS Blocks adopters.

Written by the indexing model from the issue text.