Fix tool schema generation for variadic parameters

[fengjikui]

Summary

Fixes #22134.

create_schema_from_function previously treated variadic *args and **kwargs as normal tool parameters. For functions such as:

def search(query: str, **kwargs: str) -> None: ...

this exposed a phantom kwargs property in the generated JSON schema and marked it as required, which can make strict tool/function-calling providers reject the schema.

Changes

• Skip inspect.Parameter.VAR_POSITIONAL and inspect.Parameter.VAR_KEYWORD when building tool schemas.
• Add a regression test covering *args and **kwargs, asserting only regular parameters are exposed.

Validation

• Before the fix, tests/tools/test_utils.py::test_create_schema_from_function_ignores_variadic_parameters failed because args and kwargs were present in schema properties.
• uv run --directory llama-index-core pytest tests/tools/test_utils.py -q
• uv run --directory llama-index-core pytest tests/tools/test_utils.py tests/tools/test_base.py -q
• uv run ruff format --check llama-index-core/llama_index/core/tools/utils.py llama-index-core/tests/tools/test_utils.py
• uv run ruff check llama-index-core/llama_index/core/tools/utils.py llama-index-core/tests/tools/test_utils.py

[gautamvarmadatla]

hi @fengjikui issue author here, please see #22135 it already has the fix :)