Consider migrating to 'src/` layout ('./src/circe')

[egillax]

I propose we consider moving the package from ./circe to a src/ layout (./src/circe). This is a common packaging best practice that helps avoid accidental imports from the repository root during development/testing and makes packaging behavior closer to how users import the installed distribution.

[azimov]

No objections to this, the current format is just the first thing the coding agent built. I agree that its nicer to avoid having test scripts import the circe. I will see about migrating the code today.