Add docstrings to FunctionSchema, update CONTRIBUTING.md with docstrings guidance, ignore __init__ docstrings if a class is sufficiently documented

pyproject.toml

@@ -115,6 +115,9 @@ select = [
     "D", # Docstring rules
     "I", # Import rules
 ]
+# We ignore D107 because class docstrings already document __init__ parameters
+# and our Sphinx configuration uses napoleon_include_init_with_doc=True
+ignore = ["D107"]
 
 [tool.ruff.lint.pydocstyle]
 convention = "google"