* feat: lazy compile
* refactor: lazy -> only_changed
* refactor: leave the changed function up to the user
* refactor: pass a function, based on @YannickJadoul and @HDembinski's suggestions
* refactor: old -> _old, as it's not intended for users
* docs: slight improvmenent from @rwgk
* docs: Ccache spelling, extra warning about pip caching
Ccache spelling noted by @YannickJadoul