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- Fix some type hints, in particular base tokenizer class
- Make use of `tensor.new_zero/empty` methods
- Simplify env var string parsing in launcher

Co-authored-by: Nick Hill <nickhill@us.ibm.com>

Fixes #12 in the easiest way I could think of.

AFAIK there is no torch device type called "gpu".

- Avoid theoretical hang in batcher loop
- Avoid a couple of clones in the router generate method
- Keep attention mask tensors as integers
- Remove num_heads attribute
Co-authored-by: OlivierDehaene <Olivier.dehaene@gmail.com>