Explicitly declare supported public APIs with '__all__'

### Feature Request / Improvement

Currently, we rely on the informal naming conventions (with or without underscore) to distinguish between a public or private API.

It will be helpful to declare the names of public APIs in the `__all__` attribute on all our public API supporting modules as it will:
- control what APIs we expose to wildcard imports
- enhance discoverability of public APIs (when reading the source code as users or developers)
- and allow tools like [Griffe](https://mkdocstrings.github.io/griffe/guide/users/navigating/#object-visibility) to detect the correct public APIs for backwards compatibility analysis in our CI

Empieza por identificar los módulos que admiten la API pública y revisar sus convenciones de nomenclatura actuales. Añade declaraciones de __all__ para los nombres públicos previstos; después, verifica las importaciones comodín y confirma que Griffe detecta la misma superficie de API para el análisis de compatibilidad.

Escrito por el modelo de indexación a partir del texto del issue.