fix: update PyTorch mask types and BPE tokenizer serialization

- Replace deprecated torch.uint8 and .byte() with torch.bool in GPT.generate
- Add save/load methods to BPETokenizer for proper merges and vocab_list serialization
- Update dependencies in pyproject.toml

llm/pyproject.toml

@@ -12,6 +12,13 @@ dependencies = [
     "numpy>=1.24.0",
 ]
 
+[project.optional-dependencies]
+test = [
+    "pytest>=7.0.0",
+    "pytest-cov>=4.0.0",
+    "pytest-mock>=3.0.0",
+]
+
 [build-system]
 requires = ["uv_build>=0.8.22,<0.9.0"]
 build-backend = "uv_build"