[sharktank] Depend on sentencepiece

While `gguf`'s `pyproject.toml` lists `sentencepiece` as a dependency
(https://github.com/ggerganov/llama.cpp/blob/a07c32ea54850c989f0ef6989da5b955b77b7172/pyproject.toml#L20),
the package does not get pulled in when installing gguf via `uv pip` or
`pip`. However, without the package the sanity test `python -c "from
sharktank import ops; print('Sanity check passed')"`, documented in
https://github.com/nod-ai/shark-ai/blob/main/docs/nightly_releases.md#quickstart---sharktank
fails.

sharktank/requirements.txt

@@ -5,7 +5,7 @@ gguf==0.10.0
 numpy<2.0
 
 # Needed for newer gguf versions (TODO: remove when gguf package includes this)
-# sentencepiece>=0.1.98,<=0.2.0
+sentencepiece>=0.1.98,<=0.2.0
 
 # Model deps.
 huggingface-hub==0.22.2