* EnvFactory now uses the creation of a single environment as
the basic functionality which the more high-level functions build
upon
* Introduce enum EnvMode to indicate the purpose for which an env
is created, allowing the factory creation process to change its
behaviour accordingly
* Add EnvFactoryGymnasium to provide direct support for envs that
can be created via gymnasium.make
- EnvPool is supported via an injectible EnvPoolFactory
- Existing EnvFactory implementations are now derived from
EnvFactoryGymnasium
* Use a separate environment (which uses new EnvMode.WATCH) for
watching agent performance after training (instead of using test
environments, which the user may want to configure differently)