[`LlamaTokenizer`] `tokenize` nits. (#25793)
* return when length is zero
* Add tests
Co-authored-by: Avnish Narayan <38871737avnishn@users.noreply.github.com>
* Co-authored-by: avnishn
<38871737+avnishn@users.noreply.github.com>
* codeLlama doc should not be on Main
* update test
---------
Co-authored-by: Avnish Narayan <38871737avnishn@users.noreply.github.com>
