Grid changes required

[christopherlovell]

Summary

In an ideal world, these are the updates we need to implement in the synthesizer-grids repo to get things up to scratch.

• Get all scripts running.
• Fully sanitise the package structure.
• Move all utilities to the utilities module and adjust imports.
• Remove all unused imports.
• Document functions.
• Provide a generic downloader with requests
• Make scripts safer with unyt conversions instead of magic numbers.
• Introduce tests for tools.
• Introduce a cheap integration test.