fix: multiple control flow tools same llm call

[cotovanu-cristian]

Summary

Fixes handling of multiple control flow tool calls (end_execution, raise_error) returned in a single LLM response.

The previous filter in _filter_control_flow_tool_calls was designed to strip control flow tools from mixed responses (e.g. [regular_tool, end_execution]). When the LLM returned only control flow tools (e.g. [end_execution, raise_error]), all of them got filtered out, leaving an empty
tool call list and causing a routing error — "No control flow tool call found" — in the terminate node.

Changes

_filter_control_flow_tool_calls (llm_node.py)

When the LLM response contains only control flow tools:

• If raise_error is present, keep only the first raise_error — it takes precedence over end_execution, and duplicates are collapsed
• If only end_execution calls are present, keep them as-is (single call, no filtering needed)