fix(flagtune): move PyYAML to optional dependencies

Author: k6699k

setup.py

@@ -984,7 +984,6 @@ def get_flagtree_version():
     long_description_content_type="text/markdown",
     install_requires=[
         "importlib-metadata; python_version < '3.10'",
-        *(["PyYAML>=6.0"] if helper.flagtree_backend != "thrive" else []),
     ],
     packages=list(get_packages()),
     package_dir=dict(get_package_dirs()),
@@ -1019,6 +1018,7 @@ def get_flagtree_version():
         ],
         "flagtune": [
             "numpy>=1.26.4,<2.0",
+            "PyYAML>=6.0",
             "scikit-learn>=1.4,<2.0",
             "xgboost==3.3.0",
         ],