[lamaTokenizerFast] Update documentation
# What does this PR do?
Updates the documentation for llamaFast. 
I think that long term-wise it would make more sense that the rust tokenizer updates its internals if the specials tokens are updated as well, this would allow us to remove the python layer that takes care of it. 

Related to #23889 
_The documentation is not available anymore as the PR was closed or merged._