add feature flags to config

[frolic]

We changed how we detect systems in #3649 but this change requires parsing all Solidity source files in the target source dir, which could be a bit aggressive for some projects. It'd be nice to make this functionality opt-out via config but it's unclear where to put the config option as it spans both codegen and deploy.

This brought up a discussion around adding short-lived feature flags to the config so we can add in flags for experimental features that will eventually stabilize/be a default or changed features where you may want to opt-out for backwards compat.

export default defineWorld({
  featureFlags: {
    findSystemsByInheritance: false,
  },
});