Switch to the new fs.FS over afero.FS

[miniscruff]

https://tip.golang.org/pkg/io/fs/ https://golang.org/pkg/testing/fstest/#MapFS to test

• [ ] Remove afero as a dependency
• [ ] Create interfaces for writing files as fs.FS does not include writing details. os has functions to write files though.
• [ ] Create a struct to handle mocking writes for tests to extend the memfs but with write interfaces.

[miniscruff]

May be part of a rewrite later