This change filters the scope of the public API that is provided by this
library.
Any class or interface that is not explicitly marked with an `@api`
annotation should never be used outside this library — any change can
and will be made without taking breaking changes rules into account.
When a breaking change happens inside the public API scope, a major
version will be released; refer to https://semver.org for more
information.
A new PHPStan extension is now part of the quality assurance process,
ensuring that all classes/interfaces must provide either `@internal` or
`@api` annotation.
