Unpin, clean, split dependencies

[akx]

This PR:

• unpins the Numpy upper bound dependency, to allow running on (e.g.) Python 3.13, where no precompiled version of the ancient Numpy exists
• drops the sole use of omegaconf.DictConfig in favor of a simple dict
• splits the dependencies into a couple of extras, so running the CLI examples for English or French (e.g. example_tts.py) don't require so many packages.

I tested this Works On My Machine (2023 Macbook with M2 Max, Sequoia 15.7.1, uv + Python 3.13.11).