The framework itself doesn't have any 3rd-party dependencies. Our plugins do -- but we don't force you to use the same libraries we do.
For example, we are strong advocates for Dependency Injection and we really like PHP-DI, but you are free to build your plugins using either no dependency injection at all or using a different container. Whenever the framework references dependency injection, it simply assumes that it's been passed on a PSR-11-compatible container (which should be most, if not all, popular containers) and it always provides a fallback in case no container is used at all.
That being said, the framework does have internal dependencies. It is possible to build a plugin using only the Bootstrapper Module. If you need the Helpers Module, it will auto-install the Bootstrapper Module as well when using Composer since that is listed as a dependency. Similarly, the Foundations Module depends on both the Bootstrapper and the Helpers modules, and so on.