Fix: Explicitly export public API in factory/__init__.py using __all__

[bartektrybala]

What does this PR do?

Adds the __all__ list to factory/__init__.py.

Why is this necessary?

Currently, strict type checkers (like Pyright or mypy) and modern IDEs throw an error when importing elements like LazyFunction directly from factory (e.g., "LazyFunction" is not exported from module "factory").

Explicitly defining __all__ resolves these warnings and properly defines the public API of the module without changing any underlying functionality.

Checklist:

• Code passes automated checks locally (tox)
• Resolves a single issue (type checker export warnings)

[trogers8080]

There's actually already a PR for these changes here. It just unfortunately hasn't been merged.