* switch swift-tokenizers to main, remove some workarounds
- swift-tokenizers is getting a lot of updates and fixes, let's track main for now
- remove some workarounds that are no longer needed
- https://github.com/huggingface/swift-transformers/issues/63
- document the tokenizer used (https://github.com/huggingface/swift-transformers)
- provide a hook for tokenizer configuration, prompt augmentation
- this isn't as rich as the python equivalents but it helps a little
